Questions & Answers
ICSE - Grade - 8
Subject: Physics
Chapter - 04 - Energy
Types of Questions
MCQ
- Work is said to be done when
a) Force is applied but no displacement occurs
b) Force is applied and displacement occurs in the direction of force
c) Displacement occurs without force
d) None of these
Answer: b - Which of the following is an example of work being done?
a) A boy pushing a wall
b) A person holding a bag stationary
c) A girl lifting a book from the floor
d) A man sitting on a chair
Answer: c - Work done depends on
a) Force applied and distance moved
b) Mass of object and time
c) Power and energy
d) None of these
Answer: a - Definition of work in physics is
a) Product of force and mass
b) Product of force and displacement in its direction
c) Displacement per unit time
d) Force per unit area
Answer: b - SI unit of work is
a) Newton
b) Joule
c) Watt
d) Erg
Answer: b - 1 Joule of work is done when
a) A force of 1 N moves a body by 1 m in its direction
b) A body of mass 1 kg moves by 1 m
c) Work is done in 1 second
d) None of these
Answer: a - Energy is defined as
a) Ability to apply force
b) Ability to do work
c) Product of mass and force
d) Rate of doing work
Answer: b - Relationship between work and energy is
a) Energy produces work
b) Work and energy are unrelated
c) Work done on a body is equal to the energy gained
d) Energy is always greater than work
Answer: c - Unit of energy in SI system is
a) Watt
b) Newton
c) Joule
d) Calorie
Answer: c - Mechanical energy is the sum of
a) Kinetic and heat energy
b) Potential and kinetic energy
c) Light and sound energy
d) Work and power
Answer: b - Potential energy of a body depends on its
a) Mass and velocity
b) Mass and position
c) Speed and acceleration
d) Temperature and force
Answer: b - Gravitational potential energy is possessed by a body due to its
a) Motion
b) Heat
c) Position above the ground
d) Speed
Answer: c - Example of potential energy is
a) Water stored in a dam
b) A moving car
c) A running horse
d) Sound from a bell
Answer: a - Expression for gravitational potential energy is
a) P.E. = m × g × h
b) P.E. = ½ m v²
c) P.E. = F × d
d) P.E. = m × a × t
Answer: a - Example of gravitational potential energy in daily life is
a) A stretched bow
b) A stone placed on the roof
c) A ball rolling on the ground
d) A moving bicycle
Answer: b - Kinetic energy is the energy possessed by a body due to its
a) Position
b) Temperature
c) Motion
d) Shape
Answer: c - Factors affecting kinetic energy are
a) Mass and speed of the body
b) Volume and mass of the body
c) Force and acceleration
d) Height and density
Answer: a - Expression for kinetic energy is
a) K.E. = m × g × h
b) K.E. = F × d
c) K.E. = ½ m v²
d) K.E. = m × a × v
Answer: c - A moving bullet has
a) Potential energy only
b) Kinetic energy only
c) Both potential and kinetic energy
d) No energy
Answer: b - Difference between potential energy and kinetic energy is based on
a) Position and motion
b) Speed and force
c) Work and power
d) Heat and light
Answer: a - Conversion of potential energy into kinetic energy is seen in
a) A moving car
b) Water falling from a dam
c) A running athlete
d) A hot iron rod
Answer: b - Example of potential energy changing into kinetic energy is
a) A spring releasing
b) A pendulum swinging
c) A diver jumping from a board
d) All of these
Answer: d - Different forms of energy include
a) Mechanical, electrical, heat, light, sound
b) Only kinetic and potential
c) Heat and force
d) Work and power
Answer: a - Mechanical energy can be transformed into electrical energy in
a) Dynamo
b) Electric heater
c) Microphone
d) Solar cell
Answer: a - Electrical energy is converted into mechanical energy in
a) Electric motor
b) Dynamo
c) Solar panel
d) Battery
Answer: a - Electrical energy to heat energy occurs in
a) Electric fan
b) Electric heater
c) Dynamo
d) Microphone
Answer: b - Electrical energy to sound energy occurs in
a) Loudspeaker
b) Dynamo
c) Solar cell
d) Bulb
Answer: a - Sound energy to electrical energy occurs in
a) Dynamo
b) Microphone
c) Heater
d) Bulb
Answer: b - Light energy to chemical energy occurs in
a) Photosynthesis
b) Dynamo
c) Heater
d) Solar panel
Answer: a - Electrical energy to light energy occurs in
a) Bulb
b) Microphone
c) Motor
d) Dynamo
Answer: a - Light energy to electrical energy occurs in
a) Dynamo
b) Solar cell
c) Bulb
d) Motor
Answer: b - Heat energy to mechanical energy occurs in
a) Steam engine
b) Electric motor
c) Dynamo
d) Solar cell
Answer: a - Mechanical energy to heat energy occurs in
a) Friction of brakes
b) Dynamo
c) Electric heater
d) Solar panel
Answer: a - Power is defined as
a) Work done × time
b) Rate of doing work
c) Energy stored in a body
d) Product of force and mass
Answer: b - SI unit of power is
a) Joule
b) Newton
c) Watt
d) Calorie
Answer: c - 1 Watt of power is equal to
a) 1 Joule of work done per second
b) 1 Joule of work done per minute
c) 1 Joule of work done per hour
d) 1 Joule × 1000
Answer: a - Power of a source depends on
a) Work done and time taken
b) Mass and acceleration
c) Height and velocity
d) Energy and position
Answer: a - Example of power in daily life is
a) Horsepower of engines
b) Mass of a car
c) Length of a road
d) Temperature of water
Answer: a - Difference between work and power is
a) Work is energy spent, power is rate of doing work
b) Work is rate, power is energy
c) Both are the same
d) Work depends on time, power does not
Answer: a - Difference between energy and power is
a) Energy is capacity to do work, power is rate of doing work
b) Energy is always greater than power
c) Power is stored, energy is rate
d) None of these
Answer: a - Which one is NOT an example of potential energy?
a) A stretched bow
b) A compressed spring
c) Water stored in a tank
d) A running athlete
Answer: d - Which one is NOT an example of kinetic energy?
a) Moving car
b) Flying bird
c) A person sitting quietly
d) Rolling ball
Answer: c - Energy transformation in a microphone is
a) Electrical to sound
b) Sound to electrical
c) Light to sound
d) Sound to heat
Answer: b - Energy transformation in a bulb is
a) Light to chemical
b) Electrical to light
c) Heat to sound
d) Mechanical to light
Answer: b - Energy transformation in photosynthesis is
a) Light to chemical
b) Light to heat
c) Chemical to electrical
d) Heat to mechanical
Answer: a - A pendulum at extreme position has maximum
a) Kinetic energy
b) Potential energy
c) Heat energy
d) Sound energy
Answer: b - A pendulum at mean position has maximum
a) Potential energy
b) Kinetic energy
c) Electrical energy
d) Chemical energy
Answer: b - In falling water of a dam, energy change is
a) Potential to kinetic
b) Kinetic to potential
c) Heat to light
d) Electrical to heat
Answer: a - Unit of energy used in food value is
a) Joule
b) Watt
c) Calorie
d) Newton
Answer: c - A machine of higher power does the same work in
a) Less time
b) More time
c) Equal time
d) No time
Answer: a
Fill in the Blanks
- Work is said to be done when a __________ is applied and displacement takes place in its direction.
Answer: force - If there is no displacement, the work done is __________.
Answer: zero - Lifting a bucket of water is an example of __________ being done.
Answer: work - Pushing a wall where no movement occurs means __________ work is done.
Answer: no - Work done depends on the magnitude of force and the __________ moved.
Answer: distance - The scientific definition of work is the product of force and __________ in its direction.
Answer: displacement - The SI unit of work is __________.
Answer: joule - 1 Joule of work is done when a force of 1 __________ moves a body through 1 metre.
Answer: newton - Energy is the __________ to do work.
Answer: capacity - Work done on a body is equal to the __________ gained by it.
Answer: energy - The SI unit of energy is __________.
Answer: joule - Mechanical energy is the sum of __________ energy and kinetic energy.
Answer: potential - Potential energy is the energy possessed by a body due to its __________ or configuration.
Answer: position - Gravitational potential energy is energy due to a body’s position above the __________.
Answer: ground - A stone lying on a roof has __________ energy.
Answer: potential - Expression for gravitational potential energy is __________.
Answer: m × g × h - A stretched bow possesses __________ energy.
Answer: potential - Kinetic energy is the energy possessed by a body due to its __________.
Answer: motion - The two factors affecting kinetic energy are mass and __________ of the body.
Answer: speed - The expression for kinetic energy is __________.
Answer: ½ m v² - A rolling ball possesses __________ energy.
Answer: kinetic - The energy of a moving bullet is __________ energy.
Answer: kinetic - Potential energy depends on position, while kinetic energy depends on __________.
Answer: motion - Water falling from a dam shows conversion of __________ energy into kinetic energy.
Answer: potential - A swinging pendulum demonstrates continuous transformation between potential energy and __________ energy.
Answer: kinetic - In a compressed spring, energy stored is __________ energy.
Answer: potential - Energy exists in different forms such as mechanical, heat, sound, light, and __________.
Answer: electrical - In a dynamo, mechanical energy is transformed into __________ energy.
Answer: electrical - An electric motor changes electrical energy into __________ energy.
Answer: mechanical - An electric heater changes electrical energy into __________ energy.
Answer: heat - A loudspeaker changes electrical energy into __________ energy.
Answer: sound - A microphone changes sound energy into __________ energy.
Answer: electrical - During photosynthesis, light energy is converted into __________ energy.
Answer: chemical - An electric bulb converts electrical energy into __________ energy.
Answer: light - A solar cell converts light energy into __________ energy.
Answer: electrical - A steam engine converts heat energy into __________ energy.
Answer: mechanical - Mechanical energy is converted into heat energy due to __________.
Answer: friction - Power is defined as the __________ of doing work.
Answer: rate - The SI unit of power is __________.
Answer: watt - One watt is equal to one __________ of work done per second.
Answer: joule - Power depends on the amount of work done and the __________ taken.
Answer: time - Engines are often rated in __________ power.
Answer: horse - Work is the total energy spent, while power is the __________ of doing work.
Answer: rate - Energy is the capacity to do work, while power is the __________ at which work is done.
Answer: speed - At the highest point of a pendulum swing, the energy is maximum __________ energy.
Answer: potential - At the mean position of a pendulum swing, the energy is maximum __________ energy.
Answer: kinetic - The unit of energy used in food value is __________.
Answer: calorie - 1 calorie = __________ joules.
Answer: 4.2 - A machine with greater power does the same work in __________ time.
Answer: less - Work and energy have the same SI unit, which is __________.
Answer: joule
Name the Following
- Name the condition required for work to be done.
Answer: Force must be applied and displacement must occur in its direction - Name one situation where work is not done even if force is applied.
Answer: Pushing a wall - Name one example where work is done.
Answer: Lifting a book from the floor - Name the two factors on which work done depends.
Answer: Force applied and displacement produced - Name the SI unit of work.
Answer: Joule - Name the physical quantity defined as the capacity to do work.
Answer: Energy - Name the relation between work and energy.
Answer: Work done on a body is equal to the energy gained by it - Name the SI unit of energy.
Answer: Joule - Name the two forms of mechanical energy.
Answer: Potential energy and kinetic energy - Name the type of energy possessed by a body due to its position.
Answer: Potential energy - Name the type of energy possessed by water stored in a dam.
Answer: Potential energy - Name the energy possessed by a stretched bow.
Answer: Potential energy - Name the expression for gravitational potential energy.
Answer: P.E. = m × g × h - Name the energy possessed by a stone lying on a roof.
Answer: Potential energy - Name the energy possessed by a body due to its motion.
Answer: Kinetic energy - Name two factors on which kinetic energy depends.
Answer: Mass of the body and speed of the body - Name the expression for kinetic energy.
Answer: K.E. = ½ m v² - Name the energy possessed by a moving bullet.
Answer: Kinetic energy - Name the energy possessed by a rolling ball.
Answer: Kinetic energy - Name the type of energy possessed by a flying bird.
Answer: Kinetic energy - Name the difference between potential and kinetic energy.
Answer: Potential energy depends on position, kinetic energy depends on motion - Name the energy conversion in falling water from a dam.
Answer: Potential energy into kinetic energy - Name one example where potential energy changes into kinetic energy.
Answer: Swinging pendulum - Name the energy stored in a compressed spring.
Answer: Potential energy - Name any five different forms of energy.
Answer: Mechanical, heat, electrical, light, sound - Name the device where mechanical energy is converted into electrical energy.
Answer: Dynamo - Name the device where electrical energy is converted into mechanical energy.
Answer: Electric motor - Name the device where electrical energy is converted into heat energy.
Answer: Electric heater - Name the device where electrical energy is converted into sound energy.
Answer: Loudspeaker - Name the device where sound energy is converted into electrical energy.
Answer: Microphone - Name the process where light energy is converted into chemical energy.
Answer: Photosynthesis - Name the device where electrical energy is converted into light energy.
Answer: Electric bulb - Name the device where light energy is converted into electrical energy.
Answer: Solar cell - Name the device where heat energy is converted into mechanical energy.
Answer: Steam engine - Name the situation where mechanical energy is converted into heat energy.
Answer: Friction of brakes - Name the physical quantity defined as the rate of doing work.
Answer: Power - Name the SI unit of power.
Answer: Watt - Name the definition of 1 watt.
Answer: 1 joule of work done per second - Name the two factors on which power depends.
Answer: Work done and time taken - Name the common practical unit of power for engines.
Answer: Horsepower - Name the difference between work and power.
Answer: Work is energy spent, power is the rate of doing work - Name the difference between energy and power.
Answer: Energy is the capacity to do work, power is the rate of doing work - Name the type of energy a pendulum has at its extreme position.
Answer: Potential energy - Name the type of energy a pendulum has at its mean position.
Answer: Kinetic energy - Name the unit of energy used in food value.
Answer: Calorie - Name the equivalent of 1 calorie in joules.
Answer: 4.2 joules - Name the type of machine that does the same work in less time due to higher power.
Answer: Powerful machine - Name the SI unit common to both work and energy.
Answer: Joule - Name the form of energy produced by rubbing hands together.
Answer: Heat energy - Name the transformation of energy in an electric fan.
Answer: Electrical energy to mechanical energy
Answer in One Word
- The product of force and displacement in its direction is called?
Answer: Work - The SI unit of work is?
Answer: Joule - The capacity to do work is called?
Answer: Energy - The energy possessed by a body due to its position is?
Answer: Potential - The energy possessed by a body due to its motion is?
Answer: Kinetic - The sum of potential and kinetic energy is called?
Answer: Mechanical - The SI unit of energy is?
Answer: Joule - The expression for gravitational potential energy is?
Answer: mgh - The expression for kinetic energy is?
Answer: ½mv² - The unit of food energy is?
Answer: Calorie - 1 calorie is equal to how many joules?
Answer: 4.2 - Work done per unit time is called?
Answer: Power - The SI unit of power is?
Answer: Watt - A device that converts mechanical energy into electrical energy is?
Answer: Dynamo - A device that converts electrical energy into mechanical energy is?
Answer: Motor - A device that converts electrical energy into heat energy is?
Answer: Heater - A device that converts electrical energy into sound energy is?
Answer: Loudspeaker - A device that converts sound energy into electrical energy is?
Answer: Microphone - A device that converts light energy into chemical energy is?
Answer: Photosynthesis - A device that converts electrical energy into light energy is?
Answer: Bulb - A device that converts light energy into electrical energy is?
Answer: Solar cell - A device that converts heat energy into mechanical energy is?
Answer: Steam engine - The transformation of energy that occurs due to friction is into?
Answer: Heat - The energy transformation in falling water of a dam is into?
Answer: Kinetic - The rate of doing work is called?
Answer: Power - The energy a pendulum has at its extreme position is?
Answer: Potential - The energy a pendulum has at its mean position is?
Answer: Kinetic - The energy transformation in photosynthesis is into?
Answer: Chemical - The energy transformation in a dynamo is into?
Answer: Electrical - The energy transformation in a motor is into?
Answer: Mechanical - The energy transformation in a heater is into?
Answer: Heat - The energy transformation in a loudspeaker is into?
Answer: Sound - The energy transformation in a bulb is into?
Answer: Light - The energy transformation in a solar cell is into?
Answer: Electrical - The energy transformation in a steam engine is into?
Answer: Mechanical - The physical quantity common to both work and energy is?
Answer: Joule - A stretched bow possesses which energy?
Answer: Potential - A moving bullet possesses which energy?
Answer: Kinetic - Water stored in a dam possesses which energy?
Answer: Potential - A rolling ball possesses which energy?
Answer: Kinetic - The factor other than mass affecting kinetic energy is?
Answer: Speed - The factor other than displacement affecting work is?
Answer: Force - The factor other than mass affecting potential energy is?
Answer: Height - A unit commonly used for power of engines is?
Answer: Horsepower - The physical quantity defined as “capacity to do work” is?
Answer: Energy - The physical quantity defined as “rate of doing work” is?
Answer: Power - The physical quantity defined as “force × displacement” is?
Answer: Work - The energy stored in a compressed spring is?
Answer: Potential - The SI unit of work, energy and heat is?
Answer: Joule - The SI unit of power is equivalent to one joule per?
Answer: Second
ICSE - Grade 9 - Physics
All Chapters
- Chapter 1 Measurement and Experimentation
- Chapter 2 Motion in one dimension
- Chapter 3 Laws of Motion
- Chapter 4 Pressure in fluids and Atmospheric pressure
- Chapter 5 Upthrust in Fluids, Archimedes’ Principle and Floatation
- Chapter 6 Heat and energy
- Chapter 7 Reflection of light
- Chapter 8 Propagation of Sound waves
- Chapter 9 Current Electricity
- Chapter 10 Magnetism
ICSE - Grade 9 - Chemistry
All Chapters
- Chapter 1 The Language of Chemistry
- Chapter 2 Chemical Changes and Reactions
- Chapter 3 Water
- Chapter 4 Atomic Structure and Chemical Bonding
- Chapter 5 The periodic table
- Chapter 6 Study of the first Element Hydrogen
- Chapter 7 Study of Gas laws
- Chapter 8 Atmospheric Pollution
ICSE - Grade 9 - Mathematics
All Chapters
- Chapter 1 Rational and Irrational Numbers
- Chapter 2 Compound Interest [Without Using Formula]
- Chapter 3 Compound Interest [Using Formula]
- Chapter 4 Expansions
- Chapter 5 Factorisation
- Chapter 6 Simultaneous Equations
- Chapter 7 Indices
- Chapter 8 Logarithms
- Chapter 9 Triangles
- Chapter 10 Isosceles Triangles
- Chapter 11 Inequalities
- Chapter 12 Midpoint and Its Converse
- Chapter 13 Pythagoras Theorem
- Chapter 14 Rectilinear Figures
- Chapter 15 Construction of Polygons
- Chapter 16 Area Theorems
- Chapter 17 Circle
- Chapter 18 Statistics
- Chapter 19 Mean and Median
- Chapter 20 Area and Perimeter of Plane Figures
- Chapter 21 Solids
- Chapter 22 Trigonometrical Ratios
- Chapter 23 Trigonometrical Ratios of Standard Angles
- Chapter 24 Solutions of Right Triangles
- Chapter 25 Complementary Angles
- Chapter 26 Coordinate Geometry
- Chapter 27 Graphical Solution
- Chapter 28 Distance Formula
ICSE - Grade 9 - Biology
All Chapters
- Chapter 1 Introducing Biology
- Chapter 2 Cell: The Unit Of Life
- Chapter 3 Tissues: Plant And Animal Tissue
- Chapter 4 The Flower
- Chapter 5 Pollination and Fertilization
- Chapter 6 Seeds: Structure and Germination
- Chapter 7 Respiration in Plants
- Chapter 8 Five Kingdom Classification
- Chapter 9 Economic Importance of Bacteria and Fungi
- Chapter 10 Nutrition
- Chapter 11 Digestive system
- Chapter 12 Skeleton: Movement and Locomotion
- Chapter 13 Skin: The Jack of all trades
- Chapter 14 The Respiratory System
- Chapter 15 Hygiene: [A key to Healthy Life]
- Chapter 16 Diseases: Cause and Control
- Chapter 17 Aids to Health
- Chapter 18 Health Organizations
- Chapter 19 Waste Generation and Management
ICSE - Grade 9 - History
All Chapters
- Chapter 1 – The Harappan Civilisation
- Chapter 2 – The Vedic Period
- Chapter 3 – Jainism and Buddhism
- Chapter 4 – The Mauryan Empire
- History — Chapter 5
The Sangam Age - Chapter 6 – The Age of the Guptas
- Chapter 7 – Medieval India — (A) The Cholas
- Chapter 8 – Medieval India — (B) The Delhi Sultanate
- Chapter 9 – Medieval India — (C) The Mughal Empire
- Chapter 10 – Medieval India — (D) Composite Culture
- Chapter 11 – The Modern Age in Europe — (A) Renaissance
- Chapter 12 – The Modern Age in Europe — (B) Reformation
- Chapter 13 – The Modern Age in Europe — (C) Industrial Revolution
ICSE - Grade 9 - Civics
All Chapters
- Chapter 1: Our Constitution
- Chapter 2: Salient Features of the Constitution — I
- Chapter 3: Salient Features of the
- Constitution — II
- Chapter 4: Elections
- Chapter 5: Local Self-Government — Rural
- Chapter 6: Local Self-Government — Urban
ICSE - Grade 9 - Geography
All Chapters
- Ch 1 – Earth as a Planet
Ch 2 – Geographic Grid: Latitudes and Longitudes
Ch 3 – Rotation and Revolution
Ch 4 – Earth’s Structure
Ch 5 – Landforms of the Earth
Ch 6 – Rocks
Ch 7 – Volcanoes
Ch 8 – Earthquakes
Ch 9 – Weathering
Ch 10 – Denudation
Ch 11 – Hydrosphere
Ch 12 – Composition and Structure of the Atmosphere
Ch 13 – Insolation
Ch 14 – Atmospheric Pressure and Winds
Ch 15 – Humidity
Ch 16 – Pollution
Ch 17 – Sources of Pollution
Ch 18 – Effects of Pollution
Ch 19 – Preventive Measures
Ch 20 – Natural Regions of the World
Find the Odd Man Out
- Work, Energy, Power, Temperature
Answer: Temperature
Explanation: All others are related to mechanics, temperature is a thermal concept. - Joule, Watt, Newton, Erg
Answer: Newton
Explanation: Newton is a unit of force, others are units of work, power, or energy. - Force, Work, Displacement, Velocity
Answer: Velocity
Explanation: Work depends on force and displacement, velocity is not directly related. - Potential energy, Kinetic energy, Mechanical energy, Pressure
Answer: Pressure
Explanation: Pressure is not a form of energy, others are. - mgh, ½mv², F × d, v/t
Answer: v/t
Explanation: v/t is acceleration, others are expressions for energy or work. - Dynamo, Motor, Heater, Thermometer
Answer: Thermometer
Explanation: Thermometer does not involve energy transformation, others do. - Light energy, Heat energy, Work, Kinetic energy
Answer: Work
Explanation: Work is a process, others are forms of energy. - Loudspeaker, Bulb, Solar cell, Ruler
Answer: Ruler
Explanation: Ruler does not convert energy, others are energy converters. - Photosynthesis, Solar cell, Electric bulb, Dynamo
Answer: Electric bulb
Explanation: Electric bulb converts electrical to light, others involve light in energy conversion. - Motor, Heater, Loudspeaker, Scale
Answer: Scale
Explanation: Scale is a measuring device, others are energy converters. - Potential energy, Speed, Height, Mass
Answer: Speed
Explanation: Speed does not affect potential energy, others do. - Kinetic energy, Mass, Velocity, Height
Answer: Height
Explanation: Height does not affect kinetic energy, others do. - Pendulum, Rolling ball, Moving car, Stationary book
Answer: Stationary book
Explanation: It has no kinetic energy, others have. - Calorie, Joule, Watt, Erg
Answer: Watt
Explanation: Watt is a unit of power, others are units of energy. - Solar cell, Photosynthesis, Microphone, Bulb
Answer: Microphone
Explanation: Microphone converts sound to electrical, others involve light or chemical energy. - Work, Power, Energy, Length
Answer: Length
Explanation: Length is not a mechanical quantity here, others are. - Force, Distance, Displacement, Mass
Answer: Mass
Explanation: Work depends on force and displacement, not directly on mass. - Dynamo, Motor, Heater, Friction
Answer: Friction
Explanation: Friction is a natural phenomenon, others are devices. - Potential energy, Kinetic energy, Mechanical energy, Density
Answer: Density
Explanation: Density is not a form of energy, others are. - Joule, Calorie, Erg, Newton
Answer: Newton
Explanation: Newton is force, others are energy units. - Motor, Steam engine, Bulb, Solar cell
Answer: Steam engine
Explanation: Steam engine converts heat to mechanical, others involve electrical or light. - Pendulum, Waterfall, Compressed spring, Bulb
Answer: Bulb
Explanation: Bulb involves electrical to light, others show mechanical energy conversion. - Watt, Horsepower, Joule, Kilowatt
Answer: Joule
Explanation: Joule is unit of work/energy, others are units of power. - Power, Energy, Work, Temperature
Answer: Temperature
Explanation: Temperature is not a mechanical concept, others are. - Loudspeaker, Microphone, Bulb, Fan
Answer: Fan
Explanation: Fan converts electrical to mechanical, others to sound/light. - Mass, Speed, Velocity, Height
Answer: Height
Explanation: Height does not affect kinetic energy, others do. - Work, Energy, Force, Sound
Answer: Sound
Explanation: Sound is a form of energy, others are physical quantities. - Photosynthesis, Solar cell, Dynamo, Heater
Answer: Heater
Explanation: Heater converts electrical to heat, others involve light or mechanical. - Potential energy, Kinetic energy, Heat energy, Power
Answer: Power
Explanation: Power is a rate, others are forms of energy. - Motor, Dynamo, Steam engine, Thermometer
Answer: Thermometer
Explanation: Thermometer is not related to energy conversion, others are. - Force, Displacement, Work, Watt
Answer: Watt
Explanation: Watt is unit of power, others relate to work. - Joule, Erg, Watt, Calorie
Answer: Watt
Explanation: Watt is power, others are energy units. - Velocity, Speed, Kinetic energy, Height
Answer: Height
Explanation: Height is unrelated to kinetic energy, others are. - Photosynthesis, Solar cell, Bulb, Electric motor
Answer: Electric motor
Explanation: Motor converts electrical to mechanical, others involve light energy. - Horsepower, Joule, Watt, Kilowatt
Answer: Joule
Explanation: Joule is work/energy, others are power units. - Dynamo, Microphone, Solar cell, Heater
Answer: Heater
Explanation: Heater converts electrical to heat, others to electrical. - Potential energy, Kinetic energy, Power, Mechanical energy
Answer: Power
Explanation: Power is not a form of energy, others are. - Mass, Speed, Height, Time
Answer: Time
Explanation: Time is unrelated to energy, others affect it. - Work, Power, Energy, Length
Answer: Length
Explanation: Length is not a work/energy term, others are. - Bulb, Solar cell, Loudspeaker, Stone
Answer: Stone
Explanation: Stone is not a device, others convert energy. - Calorie, Watt, Joule, Erg
Answer: Watt
Explanation: Watt is unit of power, others are energy. - Dynamo, Motor, Loudspeaker, Steam engine
Answer: Steam engine
Explanation: Steam engine uses heat, others use electrical or mechanical. - Pendulum, Spring, Rolling ball, Chair
Answer: Chair
Explanation: Chair has no energy transformation, others do. - Speed, Mass, Velocity, Density
Answer: Density
Explanation: Density does not affect kinetic energy, others do. - Photosynthesis, Solar cell, Motor, Dynamo
Answer: Motor
Explanation: Motor does not involve light energy, others do. - Erg, Calorie, Joule, Newton
Answer: Newton
Explanation: Newton is force, others are energy units. - Work, Energy, Power, Current
Answer: Current
Explanation: Current is electrical, others are mechanical. - Potential energy, Kinetic energy, Heat energy, Distance
Answer: Distance
Explanation: Distance is not a form of energy, others are. - Dynamo, Motor, Bulb, Ruler
Answer: Ruler
Explanation: Ruler is not an energy converter, others are. - Watt, Joule, Horsepower, Kilowatt
Answer: Joule
Explanation: Joule is energy, others are power.
Match the Pair
Set 1
Match the following:
- Work
B. SI unit of work
C. Condition for work to be done
D. Work = Force × ?
E. 1 Joule
Column B (shuffled):
- Product of force and displacement
- Force of 1 N displaces body by 1 m
- Joule
- Force applied and displacement in its direction
- Displacement
Correct Answers:
A-1, B-3, C-4, D-5, E-2
Set 2
Match the following:
- Energy
B. SI unit of energy
C. Relationship of work and energy
D. Energy possessed by a moving body
E. Energy possessed due to position
Column B (shuffled):
- Work and energy are interrelated
- Potential energy
- Joule
- Capacity to do work
- Kinetic energy
Correct Answers:
A-4, B-3, C-1, D-5, E-2
Set 3
Match the following:
- Gravitational potential energy
B. Expression for PE
C. Example of PE
D. Factors affecting PE
E. Stored water in dam
Column B (shuffled):
- mgh
- Mass, gravitational acceleration, height
- Energy possessed due to height
- Example of potential energy
- A real-life example of PE
Correct Answers:
A-3, B-1, C-4, D-2, E-5
Set 4
Match the following:
- Kinetic energy
B. Expression for KE
C. Factors affecting KE
D. Moving car
E. Bullet fired
Column B (shuffled):
- KE = ½ mv²
- Example of KE
- Depends on mass and velocity
- Example of KE
- Energy possessed due to motion
Correct Answers:
A-5, B-1, C-3, D-2, E-4
Set 5
Match the following:
- Potential energy
B. Kinetic energy
C. Example of PE → KE conversion
D. PE vs KE
E. Catapult
Column B (shuffled):
- Conversion of PE into KE
- Energy due to position
- Energy due to motion
- Example of PE conversion
- Difference in source of energy
Correct Answers:
A-2, B-3, C-1, D-5, E-4
Set 6
Match the following:
- Mechanical energy → Electrical energy
B. Electrical energy → Mechanical energy
C. Electrical energy → Light energy
D. Sound energy → Electrical energy
E. Light energy → Chemical energy
Column B (shuffled):
- Dynamo
- Microphone
- Fan
- Photosynthesis
- Electric bulb
Correct Answers:
A-1, B-3, C-5, D-2, E-4
Set 7
Match the following:
- Electrical energy → Heat energy
B. Electrical energy → Sound energy
C. Light energy → Electrical energy
D. Heat energy → Mechanical energy
E. Mechanical energy → Heat energy
Column B (shuffled):
- Friction
- Steam engine
- Heater
- Solar cell
- Loudspeaker
Correct Answers:
A-3, B-5, C-4, D-2, E-1
Set 8
Match the following:
- Work
B. Power
C. Unit of power
D. Work per unit time
E. 1 Watt
Column B (shuffled):
- Work done when 1 J is done in 1 second
- Watt
- Measured in joules
- Rate of doing work
- Work = Force × Displacement
Correct Answers:
A-5, B-4, C-2, D-3, E-1
Set 9
Match the following:
- Work vs Power
B. Energy vs Power
C. Work is done when…
D. Power depends on…
E. Energy definition
Column B (shuffled):
- Total effort vs rate of effort
- Work and energy capacity vs rate of doing work
- Force × displacement in same direction
- Work done and time taken
- Capacity to do work
Correct Answers:
A-1, B-2, C-3, D-4, E-5
Set 10
Match the following:
- Positive work
B. Negative work
C. Zero work
D. Example of positive work
E. Example of negative work
Column B (shuffled):
- Pushing a trolley in same direction
- Work done against displacement
- Work done when force and displacement opposite
- Lifting a load upwards
- No displacement
Correct Answers:
A-4, B-3, C-5, D-1, E-2
Short Answer Questions
- Define work.
Answer: Work is said to be done when a force is applied on a body and it gets displaced in the direction of the force. - State the condition for work to be done.
Answer: Work is done only when force is applied and displacement occurs in the direction of force. - What is the SI unit of work?
Answer: The SI unit of work is Joule (J). - Define 1 Joule of work.
Answer: Work is 1 Joule when a force of 1 N displaces a body by 1 m in the direction of force. - Is work a scalar or vector quantity?
Answer: Work is a scalar quantity. - Write the formula for work.
Answer: Work = Force × Displacement × cos θ. - Define energy.
Answer: Energy is the capacity to do work. - What is the SI unit of energy?
Answer: The SI unit of energy is Joule (J). - Name the two types of mechanical energy.
Answer: The two types of mechanical energy are potential energy and kinetic energy. - Define potential energy.
Answer: Potential energy is the energy possessed by a body due to its position or configuration. - Give an example of potential energy.
Answer: A stretched bow possesses potential energy. - Write the formula for gravitational potential energy.
Answer: Potential energy = mgh. - Define kinetic energy.
Answer: Kinetic energy is the energy possessed by a body due to its motion. - Write the formula for kinetic energy.
Answer: Kinetic energy = ½ mv². - Give one example of kinetic energy.
Answer: A moving car possesses kinetic energy. - On what factors does kinetic energy depend?
Answer: Kinetic energy depends on the mass and square of velocity of the body. - On what factors does potential energy depend?
Answer: Potential energy depends on mass, height, and gravity. - What type of energy does a stone at the top of a building have?
Answer: A stone at the top of a building has potential energy. - What type of energy does flowing water in a river possess?
Answer: Flowing water in a river possesses kinetic energy. - What type of energy does water stored in a dam possess?
Answer: Water stored in a dam possesses potential energy. - What type of energy does a flying bird have?
Answer: A flying bird has both kinetic and potential energy. - Define the law of conservation of energy.
Answer: Energy can neither be created nor destroyed, it only changes from one form to another. - Give an example of conversion of potential energy to kinetic energy.
Answer: A waterfall shows conversion of potential energy to kinetic energy. - Give an example of conversion of kinetic energy to potential energy.
Answer: A ball thrown upwards shows conversion of kinetic energy to potential energy. - What type of energy does a stretched rubber band possess?
Answer: A stretched rubber band possesses potential energy. - What type of energy does a moving bullet have?
Answer: A moving bullet has kinetic energy. - What type of energy does a wound-up clock spring possess?
Answer: A wound-up clock spring possesses potential energy. - What type of energy does a running athlete have?
Answer: A running athlete has kinetic energy. - What is the relation between work and energy?
Answer: Work done on a body is stored as its energy. - What is power?
Answer: Power is the rate of doing work. - What is the SI unit of power?
Answer: The SI unit of power is Watt (W). - Define 1 Watt of power.
Answer: A power of 1 Watt is when 1 Joule of work is done in 1 second. - State the formula of power.
Answer: Power = Work ÷ Time. - What is commercial unit of energy?
Answer: The commercial unit of energy is kilowatt-hour (kWh). - Define 1 kilowatt-hour.
Answer: 1 kWh is the energy consumed when 1 kW power is used for 1 hour. - Convert 1 kWh into Joules.
Answer: 1 kWh = 3.6 × 10⁶ Joules. - State one use of kilowatt-hour.
Answer: Kilowatt-hour is used for measuring electrical energy consumption in homes. - State one device that converts electrical energy into mechanical energy.
Answer: An electric fan converts electrical energy into mechanical energy. - State one device that converts mechanical energy into electrical energy.
Answer: A dynamo converts mechanical energy into electrical energy. - State one device that converts electrical energy into heat energy.
Answer: An electric heater converts electrical energy into heat energy. - State one device that converts electrical energy into light energy.
Answer: An electric bulb converts electrical energy into light energy. - State one device that converts sound energy into electrical energy.
Answer: A microphone converts sound energy into electrical energy. - State one device that converts electrical energy into sound energy.
Answer: A loudspeaker converts electrical energy into sound energy. - State one device that converts light energy into chemical energy.
Answer: Green plants convert light energy into chemical energy by photosynthesis. - State one device that converts light energy into electrical energy.
Answer: A solar cell converts light energy into electrical energy. - State one device that converts heat energy into mechanical energy.
Answer: A steam engine converts heat energy into mechanical energy. - What happens to energy lost due to friction?
Answer: Energy lost due to friction is converted into heat energy. - When is work done positive?
Answer: Work is positive when force and displacement are in the same direction. - When is work done negative?
Answer: Work is negative when force and displacement are in opposite directions. - When is work done zero?
Answer: Work is zero when there is no displacement or displacement is perpendicular to force.
Puzzles
- I am done when a force moves an object through a distance in the same direction; schools teach me as F × d.
Answer: Work - I am the push or pull that starts motion or causes deformation.
Answer: Force - I am the straight-line movement from one point to another used in Work = F × d.
Answer: Displacement - I am the SI unit used for work and energy; 1 of me = 1 N moved through 1 m.
Answer: Joule - I am what something must have to do work; people call me the “capacity to do work.”
Answer: Energy - I am the energy due to position or configuration — raised, stretched, or compressed.
Answer: Potential energy - I equal m × g × h for objects near Earth’s surface.
Answer: Gravitational potential energy - I am the energy of motion; faster you go, the more of me you have (½mv²).
Answer: Kinetic energy - I am the total of potential and kinetic energies in a body.
Answer: Mechanical energy - I tell how quickly work is done; W ÷ t is my formula.
Answer: Power - I am the SI unit of power; doing 1 J of work in 1 s makes one of me.
Answer: Watt - I am a device on bicycles that converts rotation into electricity for lights.
Answer: Dynamo - I convert electrical input into turning motion — fans and pumps use me.
Answer: Electric motor - I convert electrical energy into heat; people warm their rooms using me.
Answer: Electric heater - I take electrical signals and make them audible as sound.
Answer: Loudspeaker - I take sound vibrations and turn them into electrical signals for recording.
Answer: Microphone - I convert sunlight directly into electrical energy on calculators and roofs.
Answer: Solar cell - I am used by plants to change light into stored chemical food energy.
Answer: Photosynthesis - I oppose motion and turn mechanical energy into heat when two surfaces rub.
Answer: Friction - I convert high-pressure steam’s heat energy into mechanical motion.
Answer: Steam engine - I store water high above ground and thus store potential energy for electricity.
Answer: Dam - I fall from height, gain speed, and show potential energy turning to kinetic energy.
Answer: Waterfall - I swing to and fro; at the ends I have most potential, at the middle most kinetic.
Answer: Pendulum - I am stretched before release to launch an arrow — stored elastic energy inside me.
Answer: Stretched bow - I am compressed and can throw a toy when released — energy stored in my coils.
Answer: Compressed spring - I am a fast small projectile whose main energy after firing is kinetic.
Answer: Bullet - I roll down a slope and have motion-energy; children chase me in playgrounds.
Answer: Rolling ball - I measure the energy in food and equal about 4.2 joules per my small unit.
Answer: Calorie - I am the common billing unit for household electricity — 1 of me = 1 kW used for 1 hour.
Answer: Kilowatt-hour (kWh) - I spin when flowing water hits my blades and drive a generator in power plants.
Answer: Turbine - I produce electricity when a turbine turns my coils — large power stations use me.
Answer: Generator - I glow when electrical energy passes through me and emit light (and some heat).
Answer: Electric bulb - I am electrical resistance that converts electrical energy into heat in many devices.
Answer: Resistor (heating element) - I’m energy stored chemically in food or fuel that can be released by burning/metabolism.
Answer: Chemical energy - I am electrical energy turned into mechanical motion in an appliance like a fan.
Answer: Mechanical energy (as output of motor) - I am energy you hear; instruments and voices produce me.
Answer: Sound energy - I am energy you can see; sunlight and lamps are common sources.
Answer: Light energy - I am thermal energy you feel as warmth; friction and combustion produce me.
Answer: Heat energy - I am the relation that tells how much potential an object gains when lifted: mgh equals me.
Answer: Formula for gravitational potential energy - I am the formula that gives kinetic energy as half the mass times velocity squared.
Answer: ½ mv² - I am the condition when force is applied but no displacement occurs, so no work is done.
Answer: Zero work - I am the sign of work when force and displacement are opposite in direction.
Answer: Negative work - I am a device that converts sound into electrical signal for telephones.
Answer: Microphone (or transducer) - I am the process where stored energy in fuel or food becomes usable mechanical or heat energy.
Answer: Energy conversion (or transformation) - I am what remains constant in an isolated system: energy can change form but not this.
Answer: Total energy (law of conservation of energy) - I am the increase in kinetic energy when an object’s speed doubles (how many times?).
Answer: Four times (because KE ∝ v²) - I am the name given to machines’ output rating often given in horsepower.
Answer: Horsepower - I am the energy change seen when a stone on roof is released and falls to the ground.
Answer: Potential energy to kinetic energy conversion - I am the rate at which electrical appliances consume energy; you read me on your electricity bill.
Answer: Energy consumption (in kWh) - I am the practical example: device that changes flowing water’s mechanical energy into electrical energy in a hydro plant.
Answer: Hydroelectric generator
Difference Between:
- Work vs Power
Work: Work is the product of force and displacement in the direction of force. Measured in joules.
Power: Power is the rate of doing work, i.e., work done per unit time. Measured in watts. - Potential Energy vs Kinetic Energy
Potential Energy: Energy due to position or configuration. Example: Water at height.
Kinetic Energy: Energy due to motion. Example: Moving car. - Mechanical Energy vs Electrical Energy
Mechanical Energy: Sum of potential and kinetic energy in a body. Example: Pendulum.
Electrical Energy: Energy carried by moving electric charges. Example: Electric bulb. - Positive Work vs Negative Work
Positive Work: Force and displacement are in the same direction. Example: Pushing a trolley forward.
Negative Work: Force and displacement are in opposite directions. Example: Friction opposing motion. - Gravitational Potential Energy vs Elastic Potential Energy
Gravitational PE: Energy stored due to height above ground. PE = mgh.
Elastic PE: Energy stored due to deformation of spring or elastic material. PE = ½ kx². - Energy vs Power
Energy: Capacity to do work. Measured in joules.
Power: Rate of doing work. Measured in watts. - Kinetic Energy vs Work
Kinetic Energy: Energy possessed by a moving body. KE = ½ mv².
Work: Measure of energy transfer when a force moves a body. W = F × d × cos θ. - Potential Energy vs Work
Potential Energy: Stored energy due to position. PE = mgh.
Work: Energy transferred when force moves a body over a distance. - Light Energy vs Heat Energy
Light Energy: Energy transmitted in the form of light waves. Example: Sunlight.
Heat Energy: Energy transferred due to temperature difference. Example: Fire or stove. - Sound Energy vs Electrical Energy
Sound Energy: Energy transmitted via vibrations of air particles. Example: Loudspeaker.
Electrical Energy: Energy carried by moving electrons. Example: Electric fan. - Kinetic Energy vs Mechanical Energy
Kinetic Energy: Energy due to motion of a body.
Mechanical Energy: Sum of kinetic and potential energy. ME = KE + PE. - Conservation of Energy vs Transformation of Energy
Conservation of Energy: Energy cannot be created or destroyed; only changes form.
Transformation of Energy: Energy changes from one form to another. Example: PE → KE. - Friction vs Work Done Against Friction
Friction: Resistive force opposing motion between two surfaces.
Work Against Friction: Work done to overcome friction, often converted into heat. - Gravitational PE vs Kinetic Energy in Falling Body
Gravitational PE: Maximum at top of fall. PE = mgh.
Kinetic Energy: Maximum at bottom of fall. KE = ½ mv². - Chemical Energy vs Mechanical Energy
Chemical Energy: Energy stored in fuels or food, released on combustion or metabolism.
Mechanical Energy: Energy due to motion or position of a body. - Static vs Dynamic Work
Static Work: Work done without motion is zero. Example: Holding a load.
Dynamic Work: Work done with displacement in direction of force. - Unit of Work vs Unit of Power
Unit of Work: Joule (J). 1 J = 1 N × 1 m.
Unit of Power: Watt (W). 1 W = 1 J/s. - Mechanical Energy vs Electrical Energy Transformation
Mechanical Energy: Energy due to motion or position used to rotate turbines.
Electrical Energy: Generated as a result of mechanical energy in generators. - Potential Energy vs Kinetic Energy Conversion
Potential Energy: Stored energy converted to motion energy when released.
Kinetic Energy: Motion energy converted from stored potential energy. - Instantaneous Power vs Average Power
Instantaneous Power: Power at a specific instant. P = F × v.
Average Power: Total work done divided by total time. P = W/t.
Assertion and Reason
Instructions:
Each question consists of two statements: Assertion (A) and Reason (R).
Choose the correct option:
- (a) Both A and R are true, and R is the correct explanation of A
- (b) Both A and R are true, but R is not the correct explanation of A
- (c) A is true, but R is false
- (d) A is false, but R is true
Q1.
Assertion (A): Work is said to be done when a force is applied on a body and it gets displaced.
Reason (R): If there is no displacement, no work is done.
Answer: (a)
Q2.
Assertion (A): A man pushing a wall does work.
Reason (R): Work is done only when displacement takes place.
Answer: (c)
Q3.
Assertion (A): The SI unit of work is joule.
Reason (R): One joule is work done when 1 newton force displaces a body by 1 metre in the direction of force.
Answer: (a)
Q4.
Assertion (A): Energy is the capacity to do work.
Reason (R): Without energy, no work can be done.
Answer: (a)
Q5.
Assertion (A): Work and energy have the same unit.
Reason (R): Work and energy are equivalent in nature.
Answer: (a)
Q6.
Assertion (A): Mechanical energy is the sum of potential energy and kinetic energy.
Reason (R): PE is due to position and KE is due to motion.
Answer: (a)
Q7.
Assertion (A): A stretched bow has kinetic energy.
Reason (R): Energy possessed due to configuration is potential energy.
Answer: (d)
Q8.
Assertion (A): Gravitational potential energy of a body at height is given by mgh.
Reason (R): Work is required to lift a body against gravity.
Answer: (a)
Q9.
Assertion (A): A body in motion has potential energy.
Reason (R): Energy possessed due to motion is kinetic energy.
Answer: (d)
Q10.
Assertion (A): Kinetic energy depends only on mass.
Reason (R): Kinetic energy depends on both mass and velocity of the body.
Answer: (c)
Q11.
Assertion (A): Kinetic energy is expressed as ½ mv².
Reason (R): It depends directly on the square of velocity.
Answer: (a)
Q12.
Assertion (A): Potential energy is due to motion of a body.
Reason (R): Potential energy is due to position or configuration.
Answer: (d)
Q13.
Assertion (A): A stone at the top of a hill has potential energy.
Reason (R): Work was done against gravity to bring it there.
Answer: (a)
Q14.
Assertion (A): A moving car possesses kinetic energy.
Reason (R): A body in motion has energy due to velocity.
Answer: (a)
Q15.
Assertion (A): When a pendulum swings, potential energy changes into kinetic energy and back.
Reason (R): Mechanical energy remains conserved in the absence of air resistance.
Answer: (a)
Q16.
Assertion (A): At the lowest point of a pendulum swing, potential energy is maximum.
Reason (R): At this point, kinetic energy is maximum and potential energy is minimum.
Answer: (d)
Q17.
Assertion (A): The water stored in a dam has kinetic energy.
Reason (R): Stored water at height possesses potential energy.
Answer: (d)
Q18.
Assertion (A): A rolling ball possesses kinetic energy.
Reason (R): Kinetic energy depends on motion of the body.
Answer: (a)
Q19.
Assertion (A): The faster a body moves, the more kinetic energy it has.
Reason (R): Kinetic energy is proportional to the square of velocity.
Answer: (a)
Q20.
Assertion (A): Work is said to be done even when displacement is perpendicular to force.
Reason (R): Work is the product of force and displacement in the same direction.
Answer: (d)
Q21.
Assertion (A): A ball at rest on the ground has potential energy.
Reason (R): Potential energy exists due to position at a height.
Answer: (d)
Q22.
Assertion (A): The unit of energy is joule.
Reason (R): Energy and work are measured in the same unit.
Answer: (a)
Q23.
Assertion (A): Work done is equal to the energy transferred.
Reason (R): Both represent the same physical quantity.
Answer: (a)
Q24.
Assertion (A): A compressed spring has potential energy.
Reason (R): It possesses energy due to configuration.
Answer: (a)
Q25.
Assertion (A): A bullet fired from a gun possesses kinetic energy.
Reason (R): It has high velocity.
Answer: (a)
Q26.
Assertion (A): Potential energy increases as height increases.
Reason (R): PE = mgh, so it is directly proportional to height.
Answer: (a)
Q27.
Assertion (A): Energy cannot be created or destroyed.
Reason (R): Energy can only change from one form to another.
Answer: (a)
Q28.
Assertion (A): Dynamo converts mechanical energy into electrical energy.
Reason (R): Transformation of energy is possible.
Answer: (a)
Q29.
Assertion (A): Electric bulb converts electrical energy into sound energy.
Reason (R): Electric bulb converts electrical energy into light and heat.
Answer: (d)
Q30.
Assertion (A): A loudspeaker converts electrical energy into sound energy.
Reason (R): Sound energy can be produced from electricity.
Answer: (a)
Q31.
Assertion (A): Photosynthesis converts light energy into chemical energy.
Reason (R): Plants store energy in food.
Answer: (a)
Q32.
Assertion (A): Solar cell converts light energy into heat energy.
Reason (R): Solar cell converts light energy into electrical energy.
Answer: (d)
Q33.
Assertion (A): A heater converts electrical energy into heat energy.
Reason (R): Electrical resistance produces heating effect.
Answer: (a)
Q34.
Assertion (A): In a microphone, sound energy changes into electrical energy.
Reason (R): Vibrations of sound are converted into electrical signals.
Answer: (a)
Q35.
Assertion (A): Friction converts mechanical energy into heat energy.
Reason (R): Mechanical work against friction raises temperature.
Answer: (a)
Q36.
Assertion (A): Steam engine converts heat energy into mechanical energy.
Reason (R): Heat expands steam to move pistons.
Answer: (a)
Q37.
Assertion (A): Work done depends on the direction of force.
Reason (R): Work is maximum when force and displacement are in the same direction.
Answer: (a)
Q38.
Assertion (A): Power is defined as work done per unit time.
Reason (R): P = W/t.
Answer: (a)
Q39.
Assertion (A): Unit of power is Joule.
Reason (R): Power is measured in watt.
Answer: (d)
Q40.
Assertion (A): One watt is equal to one joule per second.
Reason (R): Power is the rate of doing work.
Answer: (a)
Q41.
Assertion (A): A powerful machine always does more work.
Reason (R): Power depends on work done per unit time, not only on total work.
Answer: (c)
Q42.
Assertion (A): Work and power mean the same thing.
Reason (R): Work is total effort, power is the rate of work.
Answer: (d)
Q43.
Assertion (A): Energy and power are identical quantities.
Reason (R): Energy is capacity to do work, power is rate of doing work.
Answer: (d)
Q44.
Assertion (A): Energy and work are scalar quantities.
Reason (R): They have magnitude but no direction.
Answer: (a)
Q45.
Assertion (A): Higher the power of a source, faster it can do work.
Reason (R): Power is directly proportional to work done per unit time.
Answer: (a)
Q46.
Assertion (A): A 60 W bulb consumes more energy than a 100 W bulb.
Reason (R): Power rating indicates energy consumed per unit time.
Answer: (d)
Q47.
Assertion (A): Work done can be zero even if force is applied.
Reason (R): If displacement is zero, work done is zero.
Answer: (a)
Q48.
Assertion (A): Work is positive when force and displacement are in the same direction.
Reason (R): When they are opposite, work is negative.
Answer: (a)
Q49.
Assertion (A): Kinetic energy is independent of velocity.
Reason (R): KE ∝ v².
Answer: (d)
Q50.
Assertion (A): A moving bus has both kinetic and potential energy.
Reason (R): At ground level, PE = 0, so it has only KE.
Answer: (c)
True or False
- Work is said to be done when a force is applied and displacement takes place.
Answer: True - No displacement means no work is done.
Answer: True - Work = Force ÷ Displacement.
Answer: False → Correct: Work = Force × Displacement - Work is a vector quantity.
Answer: False → Correct: Work is a scalar quantity - The SI unit of work is Joule.
Answer: True - 1 Joule is work done when 1 N force displaces a body by 1 m in its direction.
Answer: True - Energy is defined as the capacity to do work.
Answer: True - The SI unit of energy is Newton.
Answer: False → Correct: SI unit of energy is Joule - Work and energy are interrelated.
Answer: True - Mechanical energy is the sum of potential and kinetic energy.
Answer: True - Potential energy is energy due to motion.
Answer: False → Correct: Potential energy is energy due to position/configuration - Kinetic energy is energy due to motion.
Answer: True - Gravitational potential energy = mgh.
Answer: True - Kinetic energy = ½ mv.
Answer: False → Correct: Kinetic energy = ½ mv² - Potential energy depends on mass, height, and gravity.
Answer: True - Kinetic energy depends only on mass.
Answer: False → Correct: KE depends on both mass and velocity - A moving car possesses kinetic energy.
Answer: True - A stretched bow possesses kinetic energy.
Answer: False → Correct: A stretched bow possesses potential energy - A stone kept at the top of a building has potential energy.
Answer: True - A bullet fired at high speed has kinetic energy.
Answer: True - At the lowest point of a pendulum swing, potential energy is maximum.
Answer: False → Correct: At the lowest point, kinetic energy is maximum - At the highest point of a pendulum swing, kinetic energy is maximum.
Answer: False → Correct: At the highest point, potential energy is maximum - Work done on a body is stored as energy.
Answer: True - Energy and work are measured in the same unit.
Answer: True - Energy and work both are scalar quantities.
Answer: True - Energy can be created or destroyed.
Answer: False → Correct: Energy cannot be created or destroyed, only transformed - A dam stores water with kinetic energy.
Answer: False → Correct: A dam stores water with potential energy - Waterfall is an example of conversion of potential energy into kinetic energy.
Answer: True - A moving bus has both kinetic and potential energy.
Answer: True (if considered above ground level) - Photosynthesis converts light energy into electrical energy.
Answer: False → Correct: Photosynthesis converts light energy into chemical energy - Dynamo converts mechanical energy into electrical energy.
Answer: True - Fan converts electrical energy into mechanical energy.
Answer: True - Electric heater converts electrical energy into heat energy.
Answer: True - Electric bulb converts electrical energy into sound energy.
Answer: False → Correct: Electric bulb converts electrical energy into light and heat - Microphone converts sound energy into electrical energy.
Answer: True - Loudspeaker converts electrical energy into sound energy.
Answer: True - Solar cell converts light energy into heat energy.
Answer: False → Correct: Solar cell converts light energy into electrical energy - Steam engine converts heat energy into mechanical energy.
Answer: True - Friction converts mechanical energy into heat energy.
Answer: True - Work done is independent of direction of displacement.
Answer: False → Correct: Work done depends on direction of displacement - Work is positive when force and displacement are in same direction.
Answer: True - Work is negative when force and displacement are opposite.
Answer: True - Work can be zero even if force is applied.
Answer: True - Power is defined as work done per unit time.
Answer: True - SI unit of power is Joule.
Answer: False → Correct: SI unit of power is Watt - 1 Watt = 1 Joule per second.
Answer: True - Power depends only on work done, not on time taken.
Answer: False → Correct: Power depends on both work done and time taken - Work and power mean the same.
Answer: False → Correct: Work = total effort, Power = rate of doing work - Energy and power are identical.
Answer: False → Correct: Energy = capacity to do work, Power = rate of doing work - Higher the power, faster the work is done.
Answer: True
Long Answer Questions
- Define work and state the conditions necessary for work to be done.
Answer:
- Work is said to be done when a force is applied on a body and it gets displaced in the direction of force.
- Two conditions are necessary:
- A force must be applied on the body.
- The body must get displaced in the direction of the applied force.
- If there is no displacement, no work is done even if force is applied.
- Write the mathematical expression for work and explain each term.
Answer:
- Work = Force × Displacement × cos θ.
- Force is the applied force on the body.
- Displacement is the distance moved in the direction of force.
- θ is the angle between force and displacement.
- If θ = 0°, work is maximum and if θ = 90°, work done is zero.
- Define 1 Joule of work.
Answer:
- Work is 1 Joule when a force of 1 Newton displaces a body by 1 meter in the direction of the force.
- Mathematically: W = F × d = 1 N × 1 m = 1 J.
- It is the SI unit of work.
- Explain with examples when work is said to be done.
Answer:
- Work is done when a coolie lifts a load and walks in the direction of force.
- Work is done when a person pushes a car and the car moves forward.
- Work is done when a force displaces an object along its direction.
- State factors on which the amount of work done depends.
Answer:
- The magnitude of the force applied.
- The displacement produced in the body.
- The angle between force and displacement.
- If displacement is more or force is greater, work done increases.
- Define energy. State its SI unit.
Answer:
- Energy is the capacity to do work.
- The SI unit of energy is Joule (J).
- Energy exists in many forms such as potential energy, kinetic energy, heat energy, light energy, etc.
- All forms of energy can be converted into one another.
- Explain the relationship between work and energy.
Answer:
- Work and energy are closely related.
- Work done on a body is stored as its energy.
- For example, when we lift a stone, work is done and stored as potential energy.
- When the stone falls, this energy is released as kinetic energy.
- Define potential energy with an example.
Answer:
- Potential energy is the energy possessed by a body due to its position or configuration.
- Example: Water stored in a dam possesses potential energy.
- A stretched bow or compressed spring also has potential energy.
- Derive the expression for gravitational potential energy.
Answer:
- Work done = Force × Displacement.
- Force = Weight of body = mg.
- Displacement = height (h).
- Work done = mgh.
- Thus, Potential energy = mgh.
- Define kinetic energy and give an example.
Answer:
- Kinetic energy is the energy possessed by a body due to its motion.
- Example: A moving car or a flying bullet possesses kinetic energy.
- Faster moving bodies have more kinetic energy.
- Derive the expression for kinetic energy.
Answer:
- Work done on a body is equal to its kinetic energy.
- Work = Force × Displacement.
- Using equations of motion, KE = ½ mv².
- Thus, kinetic energy depends on mass and square of velocity.
- State the factors on which kinetic energy depends.
Answer:
- The mass of the body – heavier objects moving with same speed have more KE.
- The square of velocity – doubling velocity makes KE four times.
- Hence, KE ∝ mv².
- State the factors on which potential energy depends.
Answer:
- Mass of the body – heavier bodies have more potential energy at the same height.
- Height above the ground – higher objects have more PE.
- Acceleration due to gravity (g).
- Give differences between potential energy and kinetic energy.
Answer:
- Potential energy is due to position, while kinetic energy is due to motion.
- PE = mgh, KE = ½ mv².
- A stone on top of a building has PE, while a rolling stone has KE.
- Explain with examples the conversion of potential energy into kinetic energy.
Answer:
- When a stone is dropped, its potential energy converts into kinetic energy.
- In waterfalls, water at height has PE which changes into KE as it flows down.
- In a swinging pendulum, PE and KE convert into each other continuously.
- State five examples of conversion of potential energy into kinetic energy.
Answer:
- Waterfall.
- Stone falling from a height.
- A stretched bow releasing an arrow.
- A compressed spring moving a toy.
- Roller coaster moving down from the top.
- State the law of conservation of energy with an example.
Answer:
- Energy can neither be created nor destroyed; it only changes from one form to another.
- Example: In a pendulum, energy continuously converts from PE to KE but total energy remains constant.
- Give two examples of conversion of mechanical energy into electrical energy.
Answer:
- A dynamo converts mechanical energy into electrical energy.
- Hydro power plants use water’s kinetic energy to generate electricity.
- Give two examples of conversion of electrical energy into mechanical energy.
Answer:
- Electric fans.
- Electric trains.
- Give two examples of conversion of electrical energy into heat energy.
Answer:
- Electric heater.
- Electric iron.
- Give two examples of conversion of electrical energy into sound energy.
Answer:
- Loudspeakers.
- Electric bells.
- Give two examples of conversion of sound energy into electrical energy.
Answer:
- Microphone.
- Telephone.
- Give two examples of conversion of light energy into chemical energy.
Answer:
- Photosynthesis in plants.
- Solar cookers.
- Give two examples of conversion of light energy into electrical energy.
Answer:
- Solar cells.
- Solar calculators.
- Give two examples of conversion of heat energy into mechanical energy.
Answer:
- Steam engines.
- Internal combustion engines.
- Give two examples of conversion of mechanical energy into heat energy.
Answer:
- Friction of brakes in vehicles.
- Rubbing hands together.
- Define power and give its formula.
Answer:
- Power is the rate of doing work.
- Formula: Power = Work ÷ Time.
- SI unit is Watt (W).
- Define 1 Watt of power.
Answer:
- Power is 1 Watt when 1 Joule of work is done in 1 second.
- Mathematically: 1 W = 1 J/s.
- Name the factors on which power depends.
Answer:
- The total work done.
- The time taken to do the work.
- Higher work in less time means more power.
- State the difference between work and power.
Answer:
- Work is the product of force and displacement.
- Power is the rate of doing work.
- Work is measured in Joules, power in Watts.
- State the difference between energy and power.
Answer:
- Energy is the capacity to do work.
- Power is the rate at which energy is used.
- Energy is measured in Joules, power in Watts.
- Define commercial unit of energy.
Answer:
- Commercial unit of energy is kilowatt-hour (kWh).
- 1 kWh = 1000 Watt × 3600 seconds = 3.6 × 10⁶ Joules.
- It is commonly used in electricity bills.
- Explain the conversion of energy in a hydroelectric power plant.
Answer:
- Water stored at height has potential energy.
- As it flows down, PE converts to KE.
- The flowing water rotates turbines to generate electrical energy.
- Explain the energy changes in a simple pendulum.
Answer:
- At extreme position, pendulum has maximum PE and zero KE.
- At mean position, pendulum has maximum KE and zero PE.
- Total energy remains constant at all times.
- What happens to work done against friction?
Answer:
- Work done against friction is converted into heat energy.
- Example: Vehicle brakes become hot due to friction.
- Why is energy said to be conserved?
Answer:
- Because energy cannot be created or destroyed.
- It only changes form.
- The total energy of an isolated system always remains constant.
- What type of energy transformation takes place in an electric bulb?
Answer:
- Electrical energy is converted into light energy.
- Some part is also converted into heat energy.
- What type of energy transformation takes place in a microphone?
Answer:
- Sound energy is converted into electrical energy.
- What type of energy transformation takes place in a solar cell?
Answer:
- Light energy is converted into electrical energy.
- What type of energy transformation takes place in photosynthesis?
Answer:
- Light energy from the sun is converted into chemical energy in plants.
- Give an example of multiple energy conversions in a device.
Answer:
- In an electric fan: Electrical energy → Mechanical energy → Heat energy due to friction.
- Explain positive, negative, and zero work with examples.
Answer:
- Positive work: When force and displacement are in the same direction (pushing a cart forward).
- Negative work: When force and displacement are opposite (friction).
- Zero work: When no displacement occurs (pushing a wall).
- How does mass of a body affect its kinetic energy?
Answer:
- KE = ½ mv².
- If velocity is constant, doubling mass doubles KE.
- Heavier bodies have more KE when moving at same speed.
- How does velocity of a body affect its kinetic energy?
Answer:
- KE ∝ v².
- If velocity is doubled, KE becomes four times.
- Thus velocity affects KE more strongly than mass.
- Give an example of transformation of energy in a hydro turbine.
Answer:
- Water at height (PE) → Flowing water (KE) → Turbine rotation (mechanical energy) → Generator (electrical energy).
- What type of energy is stored in a stretched spring? How can it be released?
Answer:
- A stretched spring has potential energy.
- It can be released as kinetic energy when the spring is let go.
- Explain the working of a steam engine in terms of energy.
Answer:
- Coal burns to produce heat energy.
- Heat energy converts water into steam.
- Steam pressure moves the piston, converting heat energy into mechanical energy.
- Why does a moving vehicle have more kinetic energy than a slower vehicle of same mass?
Answer:
- Because KE ∝ v².
- Greater speed means more kinetic energy.
- What type of energy transformation takes place in an electric heater?
Answer:
- Electrical energy is converted into heat energy.
- Why is work done considered zero when displacement is perpendicular to force?
Answer:
- Work = F × d × cos θ.
- If θ = 90°, cos 90° = 0.
- Hence, work done = 0.
Give Reasons
- Give reason why no work is done when you push a wall.
Answer: No work is done because the wall does not get displaced even though force is applied. - Give reason why work done is zero when force is applied at 90° to displacement.
Answer: Work = F × d × cos θ, and cos 90° = 0, so work = 0. - Give reason why carrying a load on your head while walking horizontally does not involve work.
Answer: Force acts vertically upward while displacement is horizontal, so θ = 90°, work = 0. - Give reason why work done is considered positive when force and displacement are in the same direction.
Answer: Because cos θ = 1, hence work = F × d, which is positive. - Give reason why work done against friction is considered negative.
Answer: Because force of friction acts opposite to displacement, so θ = 180°, cos θ = -1. - Give reason why energy is called the capacity to do work.
Answer: Because a body with energy can apply force and cause displacement, which means work can be done. - Give reason why a stretched bow possesses potential energy.
Answer: Because of its stretched position, the bow has energy stored due to its configuration. - Give reason why water stored in a dam has potential energy.
Answer: Because it is at a height above ground, so it has energy due to position (mgh). - Give reason why a moving bullet has kinetic energy.
Answer: Because it is in motion and KE = ½ mv². - Give reason why faster moving objects have more kinetic energy.
Answer: Because KE ∝ v², so doubling velocity makes KE four times. - Give reason why heavier objects at the same height have more potential energy.
Answer: Because PE = mgh, and greater mass means greater PE. - Give reason why a body raised to a greater height possesses more potential energy.
Answer: Because PE depends directly on height (h). - Give reason why potential energy is considered stored energy.
Answer: Because it is energy possessed by a body due to its position or configuration, not motion. - Give reason why kinetic energy increases with velocity.
Answer: Because velocity is squared in the formula KE = ½ mv², making it more influential. - Give reason why kinetic energy is always positive.
Answer: Because mass and square of velocity are always positive quantities. - Give reason why energy can neither be created nor destroyed.
Answer: Because of the law of conservation of energy; it only changes form. - Give reason why pendulum energy is conserved.
Answer: Potential energy converts into kinetic energy and vice versa, but total energy remains constant. - Give reason why a ball thrown upwards comes down.
Answer: Its kinetic energy gradually converts into potential energy, and then gravity brings it back. - Give reason why waterfalls are used in hydroelectric power plants.
Answer: Waterfalls convert potential energy of water into kinetic energy to rotate turbines. - Give reason why dynamo is used in bicycles.
Answer: Because it converts mechanical energy of motion into electrical energy for lighting. - Give reason why solar cells are used in calculators.
Answer: Because they convert light energy directly into electrical energy. - Give reason why a moving fan becomes hot after use.
Answer: Because some mechanical energy is lost as heat due to friction in its parts. - Give reason why an electric bulb gives both light and heat energy.
Answer: Because electrical energy is converted into light energy and part of it into heat energy. - Give reason why a loudspeaker works when electricity is supplied.
Answer: Because electrical energy is converted into sound energy. - Give reason why microphones are used in sound recording.
Answer: Because they convert sound energy into electrical energy. - Give reason why rubbing hands together produces heat.
Answer: Because mechanical energy of motion is converted into heat energy due to friction. - Give reason why brakes of vehicles get heated.
Answer: Because kinetic energy of motion is converted into heat energy by friction in brakes. - Give reason why hydroelectric power plants are environment friendly.
Answer: Because they use renewable water energy without pollution. - Give reason why electrical energy is called the most convenient form of energy.
Answer: Because it can be easily transformed into other forms like heat, light, and motion. - Give reason why commercial unit of energy is kilowatt-hour.
Answer: Because joule is too small for practical measurement of electrical energy consumption. - Give reason why electricity bills are calculated in kWh instead of joules.
Answer: Because kWh represents larger quantities, making calculation easier. - Give reason why 1 kWh = 3.6 × 10⁶ J.
Answer: Because 1 kW = 1000 W and 1 hour = 3600 s, so 1000 × 3600 = 3.6 × 10⁶ J. - Give reason why steam engines were widely used in olden days.
Answer: Because they converted heat energy of steam into mechanical energy to run machines. - Give reason why potential and kinetic energy are called mechanical energies.
Answer: Because they arise due to position and motion of a body. - Give reason why power is called the rate of doing work.
Answer: Because power is calculated by dividing work done by time taken. - Give reason why 1 Watt is defined as 1 Joule per second.
Answer: Because power is work per unit time, so 1 W = 1 J/s. - Give reason why an athlete running fast has high kinetic energy.
Answer: Because KE depends on the square of velocity, and faster speed gives more energy. - Give reason why a stretched spring can move a toy when released.
Answer: Because its potential energy converts into kinetic energy. - Give reason why energy transformations are not 100% efficient.
Answer: Because some energy is always lost as heat or sound due to friction or resistance. - Give reason why work is done when a load is lifted.
Answer: Because an upward force is applied and displacement takes place in direction of force. - Give reason why work done against gravity is stored as potential energy.
Answer: Because lifting a body to a height gives it energy due to position (mgh). - Give reason why kinetic energy becomes zero at the top of a vertical throw.
Answer: Because velocity becomes zero at the highest point. - Give reason why potential energy of a ball is maximum at the highest point in its motion.
Answer: Because it has maximum height and zero kinetic energy at that point. - Give reason why KE is greater factor of velocity than mass.
Answer: Because KE depends on square of velocity, while it depends linearly on mass. - Give reason why a stone dropped from a height speeds up as it falls.
Answer: Because its potential energy is continuously converted into kinetic energy. - Give reason why electric heater becomes hot when current flows.
Answer: Because electrical energy is converted into heat energy due to resistance of wire. - Give reason why a person feels tired even if no work is done on wall.
Answer: Because body energy is used internally, though no mechanical work is done. - Give reason why machines are designed to reduce friction.
Answer: Because friction converts mechanical energy into unwanted heat energy, wasting energy. - Give reason why water at the bottom of a dam flows with high speed.
Answer: Because its potential energy converts into kinetic energy as it falls. - Give reason why total energy of an isolated system remains constant.
Answer: Because according to the law of conservation of energy, energy can only change form, not be destroyed.
Arrange the Words
Case Studies
- Case Study: A boy lifts a bucket of water from the ground to a height of 2 m.
Question: Calculate the work done if the bucket weighs 10 N.
Answer: Work done = F × d = 10 × 2 = 20 J - Case Study: A car moves at a speed of 10 m/s with a mass of 500 kg.
Question: Calculate its kinetic energy.
Answer: KE = ½ mv² = ½ × 500 × 10² = 25,000 J - Case Study: Water stored at 50 m height in a dam is released. Mass = 200 kg.
Question: Find the potential energy of the water. (g = 10 m/s²)
Answer: PE = mgh = 200 × 10 × 50 = 100,000 J - Case Study: A fan motor consumes 60 J of electrical energy in 2 seconds.
Question: Find the power of the motor.
Answer: Power = Work/Time = 60/2 = 30 W - Case Study: A moving ball of mass 2 kg has a velocity of 5 m/s.
Question: Find its kinetic energy.
Answer: KE = ½ mv² = ½ × 2 × 5² = 25 J - Case Study: A child stretches a spring by 0.5 m with a force of 20 N.
Question: Find the work done in stretching the spring.
Answer: Work = F × d = 20 × 0.5 = 10 J - Case Study: A pendulum of mass 2 kg is raised to a height of 1.5 m.
Question: Find its potential energy.
Answer: PE = mgh = 2 × 10 × 1.5 = 30 J - Case Study: A hydroelectric turbine rotates and generates 5000 J of electricity in 5 seconds.
Question: Find the power output.
Answer: Power = Work/Time = 5000/5 = 1000 W - Case Study: A moving car comes to rest due to friction. Its kinetic energy was 50,000 J.
Question: Into what energy is this converted?
Answer: It is converted into heat energy due to friction. - Case Study: A battery powers a bulb for 2 hours, consuming 100 W.
Question: Find the energy consumed in kWh.
Answer: Energy = Power × Time = 100 × 2 = 200 Wh = 0.2 kWh - Case Study: A bow is stretched with a force of 50 N over 0.3 m.
Question: Find the work done in stretching the bow.
Answer: Work = F × d = 50 × 0.3 = 15 J - Case Study: A 0.5 kg stone falls from 10 m height.
Question: Find its potential energy at the top. (g = 10 m/s²)
Answer: PE = mgh = 0.5 × 10 × 10 = 50 J - Case Study: A car engine does 20,000 J of work in 10 seconds.
Question: Find the power developed by the engine.
Answer: Power = Work/Time = 20,000/10 = 2000 W - Case Study: A 5 kg body moves at 4 m/s on a frictionless surface.
Question: Find its kinetic energy.
Answer: KE = ½ mv² = ½ × 5 × 4² = 40 J - Case Study: A student uses a hand-cranked dynamo to light a bulb.
Question: Name the energy transformations involved.
Answer: Mechanical energy → Electrical energy → Light energy - Case Study: Water at the top of a hill has mass 100 kg and height 30 m.
Question: Find potential energy.
Answer: PE = mgh = 100 × 10 × 30 = 30,000 J - Case Study: A car brakes and stops. The kinetic energy lost is 80,000 J.
Question: What happens to this energy?
Answer: Converted into heat energy due to friction between brakes and wheels. - Case Study: A spring is compressed by 0.4 m with a force of 25 N.
Question: Work done on the spring?
Answer: Work = F × d = 25 × 0.4 = 10 J - Case Study: A cyclist pedals with a force of 50 N over 20 m in 10 s.
Question: Find work done and power.
Answer: Work = F × d = 50 × 20 = 1000 J; Power = 1000/10 = 100 W - Case Study: A pendulum swings down from 2 m height. Mass = 1 kg.
Question: Calculate potential energy at the top and kinetic energy at the bottom. (g = 10 m/s²)
Answer: PE top = mgh = 1 × 10 × 2 = 20 J; KE bottom = 20 J (PE converts to KE).
Numericals
- Problem: A boy lifts a 10 kg box to a height of 2 m. Find the work done. (g = 10 m/s²)
Answer: Work done = Force × Distance = Weight × Height = mg × h = 10 × 10 × 2 = 200 J - Problem: A body of mass 5 kg moves with a speed of 4 m/s. Find its kinetic energy.
Answer: KE = ½ mv² = ½ × 5 × 4² = ½ × 5 × 16 = 40 J - Problem: Water of mass 50 kg is stored at a height of 10 m. Find its potential energy. (g = 10 m/s²)
Answer: PE = mgh = 50 × 10 × 10 = 5000 J - Problem: A force of 20 N moves a box 5 m on a frictionless surface. Find the work done.
Answer: W = F × d = 20 × 5 = 100 J - Problem: A car of mass 500 kg moves with a speed of 10 m/s. Calculate its kinetic energy.
Answer: KE = ½ mv² = ½ × 500 × 10² = 2500 × 10 = 25,000 J - Problem: A spring is stretched by 0.3 m by a force of 50 N. Find the work done.
Answer: W = F × d = 50 × 0.3 = 15 J - Problem: A hydroelectric turbine generates 6000 J of electrical energy in 3 seconds. Find power.
Answer: P = W/t = 6000/3 = 2000 W - Problem: A stone of mass 2 kg falls from 5 m. Find the potential energy at the top.
Answer: PE = mgh = 2 × 10 × 5 = 100 J - Problem: A car does 50,000 J of work in 10 seconds. Find the power developed.
Answer: P = W/t = 50,000/10 = 5000 W - Problem: A 2 kg body moves at 6 m/s. Find kinetic energy.
Answer: KE = ½ mv² = ½ × 2 × 36 = 36 J - Problem: A boy lifts a 15 kg bag to a height of 3 m. Find work done.
Answer: W = mgh = 15 × 10 × 3 = 450 J - Problem: A pendulum of mass 1 kg is raised to 2 m. Find its potential energy.
Answer: PE = mgh = 1 × 10 × 2 = 20 J - Problem: A 0.5 kg stone falls from 4 m. Find KE just before hitting the ground.
Answer: PE at top = mgh = 0.5 × 10 × 4 = 20 J. At bottom KE = 20 J - Problem: A force of 30 N moves a block 6 m along the floor. Work done?
Answer: W = F × d = 30 × 6 = 180 J - Problem: A car engine delivers 10,000 J of work in 5 s. Find power.
Answer: P = W/t = 10,000/5 = 2000 W - Problem: A 3 kg ball rolls at 5 m/s. Find kinetic energy.
Answer: KE = ½ mv² = ½ × 3 × 25 = 37.5 J - Problem: A 10 kg object is lifted 4 m. Find work done.
Answer: W = mgh = 10 × 10 × 4 = 400 J - Problem: Water of mass 100 kg is at height 20 m. Find potential energy.
Answer: PE = mgh = 100 × 10 × 20 = 20,000 J - Problem: A fan motor consumes 120 J in 4 s. Find power.
Answer: P = W/t = 120/4 = 30 W - Problem: A stone of mass 0.2 kg is thrown up with speed 5 m/s. Find KE at release.
Answer: KE = ½ mv² = ½ × 0.2 × 25 = 2.5 J - Problem: A spring is compressed 0.2 m with a force of 40 N. Work done?
Answer: W = F × d = 40 × 0.2 = 8 J - Problem: A car of mass 400 kg moves at 8 m/s. Find kinetic energy.
Answer: KE = ½ mv² = ½ × 400 × 64 = 12,800 J - Problem: A child climbs stairs of height 5 m with mass 30 kg. Work done?
Answer: W = mgh = 30 × 10 × 5 = 1500 J - Problem: Water of mass 200 kg falls from 10 m. Find potential energy.
Answer: PE = mgh = 200 × 10 × 10 = 20,000 J - Problem: A car brakes and stops; initial KE = 40,000 J. Where does this energy go?
Answer: Converted into heat energy due to friction. - Problem: A body of mass 2 kg is raised to 5 m. Find potential energy.
Answer: PE = mgh = 2 × 10 × 5 = 100 J - Problem: A stone of mass 1 kg falls from 3 m. KE at bottom?
Answer: KE = PE at top = mgh = 1 × 10 × 3 = 30 J - Problem: A fan consumes 60 J in 2 s. Power developed?
Answer: P = W/t = 60/2 = 30 W - Problem: A spring stretched by 0.5 m with force 25 N. Work done?
Answer: W = F × d = 25 × 0.5 = 12.5 J - Problem: A car moves at 20 m/s with mass 800 kg. KE?
Answer: KE = ½ mv² = ½ × 800 × 400 = 160,000 J - Problem: Water of mass 50 kg at height 15 m. PE?
Answer: PE = mgh = 50 × 10 × 15 = 7500 J - Problem: A bulb consumes 100 J in 5 s. Power?
Answer: P = W/t = 100/5 = 20 W - Problem: A ball of mass 0.4 kg rolls at 3 m/s. KE?
Answer: KE = ½ mv² = ½ × 0.4 × 9 = 1.8 J - Problem: A boy lifts a 12 kg bag to 2 m. Work done?
Answer: W = mgh = 12 × 10 × 2 = 240 J - Problem: A stone falls from 8 m. Mass = 1 kg. Find KE at bottom.
Answer: KE = mgh = 1 × 10 × 8 = 80 J - Problem: A car does 25,000 J of work in 10 s. Power?
Answer: P = W/t = 25,000/10 = 2500 W - Problem: A moving ball has KE = 100 J, mass = 2 kg. Find speed.
Answer: KE = ½ mv² → 100 = 1 × v² → v² = 100 → v = 10 m/s - Problem: Water of mass 150 kg at 12 m. PE?
Answer: PE = mgh = 150 × 10 × 12 = 18,000 J - Problem: A fan motor consumes 180 J in 6 s. Power?
Answer: P = W/t = 180/6 = 30 W - Problem: A spring compressed 0.4 m with force 30 N. Work done?
Answer: W = F × d = 30 × 0.4 = 12 J - Problem: A car of mass 600 kg moves at 15 m/s. KE?
Answer: KE = ½ × 600 × 225 = 67,500 J - Problem: A child climbs height 6 m. Mass = 25 kg. Work done?
Answer: W = mgh = 25 × 10 × 6 = 1500 J - Problem: A pendulum of mass 1.5 kg raised to 2 m. PE?
Answer: PE = mgh = 1.5 × 10 × 2 = 30 J - Problem: A stone of mass 0.8 kg falls from 5 m. KE at bottom?
Answer: KE = mgh = 0.8 × 10 × 5 = 40 J - Problem: A car engine does 15,000 J work in 15 s. Power?
Answer: P = W/t = 15,000/15 = 1000 W - Problem: A ball of mass 3 kg moves at 8 m/s. KE?
Answer: KE = ½ × 3 × 64 = 96 J - Problem: A body of mass 4 kg is lifted 3 m. Work done?
Answer: W = mgh = 4 × 10 × 3 = 120 J - Problem: Water of mass 250 kg at 20 m. PE?
Answer: PE = mgh = 250 × 10 × 20 = 50,000 J - Problem: A spring stretched by 0.6 m with force 20 N. Work done?
Answer: W = F × d = 20 × 0.6 = 12 J - Problem: A car moves at 12 m/s with mass 500 kg. KE?
Answer: KE = ½ mv² = ½ × 500 × 144 = 36,000 J
Find out free resources that you need.
ICSE
Grade 8
Grade 9
CBSE
Grade 8
Grade 9
Subjects we teach
“Arise, awake, and learn by approaching the excellent teachers”
Shiksha Marg 108 gives you all free resources to ensure you get the best results. Get ready for you ICSE and CBSE exams!.
