ICSE – Grade 8 – Physics – Ch 02 – QA

Questions & Answers

ICSE - Grade - 8

Subject: Physics

Chapter - 02 - Physical Quantities and Measurement

Types of Questions

MCQ

  1. What is the S.I. unit of density?
    (a) g/cm³
    (b) kg/cm³
     (c) kg/m³
     (d) g/m³
     Answer: (c) kg/m³
  2. What is the C.G.S. unit of density?
    (a) kg/m³
    (b) g/m³
     (c) g/cm³
     (d) kg/cm³
     Answer: (c) g/cm³
  3. The density of water in C.G.S. units is:
    (a) 1000 g/cm³
    (b) 1 g/cm³
     (c) 10 g/cm³
     (d) 0.1 g/cm³
     Answer: (b) 1 g/cm³
  4. Relative density is a:
    (a) Scalar quantity with units
    (b) Scalar quantity without units
     (c) Vector quantity with units
     (d) Vector quantity without units
     Answer: (b) Scalar quantity without units
  5. What is the formula for density?
    (a) Mass × Volume
    (b) Mass / Volume
     (c) Volume / Mass
     (d) Volume × Area
     Answer: (b) Mass / Volume
  6. Which instrument is used to measure the volume of an irregular solid?
    (a) Thermometer
    (b) Vernier calliper
     (c) Eureka can
     (d) Barometer
     Answer: (c) Eureka can
  7. Which of the following substances floats in water?
    (a) Iron
    (b) Ice
     (c) Gold
     (d) Lead
     Answer: (b) Ice
  8. If the density of a substance is 13.6 g/cm³, it is likely to be:
    (a) Ice
    (b) Wood
     (c) Mercury
     (d) Water
     Answer: (c) Mercury
  9. A body sinks in a liquid when its:
    (a) Density < liquid
    (b) Volume > liquid
     (c) Density > liquid
     (d) Surface area < liquid
     Answer: (c) Density > liquid
  10. The law of flotation states:
    (a) A body floats if its volume is maximum
    (b) A body displaces equal mass of water
     (c) A floating body displaces its own weight of liquid
     (d) A body floats if it is hollow
     Answer: (c) A floating body displaces its own weight of liquid
  11. What is the density of ice?
    (a) 1.2 g/cm³
    (b) 1 g/cm³
     (c) 0.92 g/cm³
     (d) 0.82 g/cm³
     Answer: (c) 0.92 g/cm³
  12. Which of the following is not a vessel for measuring volume?
    (a) Measuring cylinder
    (b) Beaker
     (c) Barometer
     (d) Eureka can
     Answer: (c) Barometer
  13. Which property allows a ship made of iron to float?
    (a) High speed
    (b) Large surface area
     (c) Shape and volume
     (d) Density less than water
     Answer: (d) Density less than water
  14. Relative density of a substance is:
    (a) Always more than 1
    (b) Always less than 1
     (c) Ratio of its density to that of water
     (d) Sum of density and weight
     Answer: (c) Ratio of its density to that of water
  15. Which of these has no unit?
    (a) Density
    (b) Volume
     (c) Mass
     (d) Relative density
     Answer: (d) Relative density
  16. What is the unit of volume in the S.I. system?
    (a) cm³
    (b) m²
     (c) m³
     (d) dm³
     Answer: (c) m³
  17. The density of gold is approximately:
    (a) 10 g/cm³
    (b) 19.3 g/cm³
     (c) 2.5 g/cm³
     (d) 5 g/cm³
     Answer: (b) 19.3 g/cm³
  18. The principle of flotation is based on:
    (a) Newton’s third law
    (b) Archimedes’ principle
     (c) Law of inertia
     (d) Pascal’s law
     Answer: (b) Archimedes’ principle
  19. Which is heavier: 1 cm³ of gold or 1 cm³ of iron?
    (a) Gold
    (b) Iron
     (c) Both same
     (d) Cannot say
     Answer: (a) Gold
  20. Which of the following is not a method of measuring mass?
    (a) Spring balance
    (b) Beam balance
     (c) Digital balance
     (d) Eureka can
     Answer: (d) Eureka can
  21. Which liquid is used in a density bottle experiment?
    (a) Mercury
    (b) Water
     (c) Petrol
     (d) Acid
     Answer: (b) Water
  22. Density of a substance changes with:
    (a) Volume only
    (b) Mass only
     (c) State of matter
     (d) Shape
     Answer: (c) State of matter
  23. Volume of regular solid is calculated using:
    (a) Displacement method
    (b) Geometric formula
     (c) Archimedes’ law
     (d) Stopwatch
     Answer: (b) Geometric formula
  24. Relative density of kerosene is:
    (a) 1.1
    (b) 0.8
     (c) 1.0
     (d) 1.6
     Answer: (b) 0.8
  25. A stone displaces 80 cm³ of water. Its volume is:
    (a) 8 cm³
    (b) 80 cm³
     (c) 0.8 cm³
     (d) 800 cm³
     Answer: (b) 80 cm³
  26. If relative density of a substance is 0.7, it will:
    (a) Sink in water
    (b) Float on water
     (c) Float just below water surface
     (d) Float in air
     Answer: (b) Float on water
  27. Eureka can works on the principle of:
    (a) Refraction
    (b) Buoyancy
     (c) Reflection
     (d) Inertia
     Answer: (b) Buoyancy
  28. The density of iron is approximately:
    (a) 7.8 g/cm³
    (b) 6.3 g/cm³
     (c) 2.1 g/cm³
     (d) 1.0 g/cm³
     Answer: (a) 7.8 g/cm³
  29. What quantity is measured in cm³?
    (a) Time
    (b) Volume
     (c) Force
     (d) Area
     Answer: (b) Volume
  30. What is the volume of water displaced by a body of 500 g and density 5 g/cm³?
    (a) 100 cm³
    (b) 50 cm³
     (c) 5 cm³
     (d) 25 cm³
     Answer: (a) 100 cm³
  31. Volume of water in density bottle = 50 g. Volume of oil in same bottle = 40 g. Relative density = ?
    (a) 1.2
    (b) 0.8
     (c) 1.0
     (d) 0.9
     Answer: (b) 0.8
  32. A balloon rises in air due to:
    (a) Weight of balloon
    (b) Gravity
     (c) Density of helium less than air
     (d) Density of helium greater than air
     Answer: (c) Density of helium less than air
  33. SI unit of mass is:
    (a) gram
    (b) tonne
     (c) kilogram
     (d) milligram
     Answer: (c) kilogram
  34. One cubic meter =
    (a) 100 cm³
    (b) 1000 cm³
     (c) 10⁶ cm³
     (d) 10⁴ cm³
     Answer: (c) 10⁶ cm³
  35. Which of these will displace most water when submerged?
    (a) 10 g iron
    (b) 10 g wood
     (c) 10 g gold
     (d) All equal
     Answer: (b) 10 g wood
  36. What helps a whale float in water?
    (a) Speed
    (b) Muscles
     (c) Lungs filled with air
     (d) Bones
     Answer: (c) Lungs filled with air
  37. Submarine floats by:
    (a) Reducing speed
    (b) Increasing temperature
     (c) Changing buoyant force using ballast tanks
     (d) Using heavy propellers
     Answer: (c) Changing buoyant force using ballast tanks
  38. In density bottle, excess liquid:
    (a) Increases pressure
    (b) Is retained
     (c) Escapes through the hole
     (d) Freezes
     Answer: (c) Escapes through the hole
  39. Density = 12 g/cm³, volume = 3 cm³, mass = ?
    (a) 4 g
    (b) 36 g
     (c) 9 g
     (d) 15 g
     Answer: (b) 36 g
  40. Ice floats in water because:
    (a) Ice is heavier
    (b) Ice has lower temperature
     (c) Ice has lower density
     (d) Ice expands
     Answer: (c) Ice has lower density
  41. What type of quantity is density?
    (a) Scalar
    (b) Vector
     (c) Tensor
     (d) Derived vector
     Answer: (a) Scalar
  42. In density bottle method, volume is assumed to be equal to:
    (a) Water lost
    (b) Water gained
     (c) Mass of air
     (d) Mass of stopper
     Answer: (a) Water lost
  43. Density of air is:
    (a) 1.29 kg/m³
    (b) 10.29 kg/m³
     (c) 1290 kg/m³
     (d) 1000 kg/m³
     Answer: (a) 1.29 kg/m³
  44. A floating body will displace:
    (a) Its volume of water
    (b) Its mass of water
     (c) Its weight of water
     (d) Its area of water
     Answer: (c) Its weight of water
  45. The device used to measure small fixed volume is:
    (a) Thermometer
    (b) Density bottle
     (c) Measuring tape
     (d) Compass
     Answer: (b) Density bottle
  46. A wooden log floats because:
    (a) It is long
    (b) It is dry
     (c) Its density is less than water
     (d) It is rough
     Answer: (c) Its density is less than water
  47. If RD > 1, substance will:
    (a) Float
    (b) Sink
     (c) Remain suspended
     (d) Evaporate
     Answer: (b) Sink
  48. The mass of 1 cm³ of water is:
    (a) 10 g
    (b) 0.1 g
     (c) 100 g
     (d) 1 g
     Answer: (d) 1 g
  49. If a solid weighs 120 g and displaces 100 cm³ of water, its density is:
    (a) 1.2 g/cm³
    (b) 1.0 g/cm³
     (c) 0.8 g/cm³
     (d) 2.0 g/cm³
     Answer: (a) 1.2 g/cm³
  50. What happens when a body’s weight < buoyant force?
    (a) Sinks
    (b) Floats partially
     (c) Floats fully
     (d) Remains suspended
     Answer: (b) Floats partially

Fill in the Blanks

  1. The S.I. unit of density is _______.
    Answer: kg/m³
  2. The C.G.S. unit of density is _______.
    Answer: g/cm³
  3. Density = _______ ÷ Volume.
    Answer: Mass
  4. Relative density is the ratio of density of a substance to the density of _______.
    Answer: water
  5. Relative density has _______ unit.
    Answer: no
  6. 1 g/cm³ = _______ kg/m³.
    Answer: 1000
  7. A body floats if its density is _______ than the density of liquid.
    Answer: less
  8. The volume of an irregular solid can be measured using a _______.
    Answer: Eureka can
  9. A body sinks in a liquid if its density is _______ than that of the liquid.
    Answer: more
  10. Ice floats in water because its density is _______ than that of water.
    Answer: less
  11. The principle of flotation is based on _______ principle.
    Answer: Archimedes’
  12. A _______ is used to measure the volume of a liquid accurately.
    Answer: measuring cylinder
  13. The law of flotation states that a floating body displaces its own _______ of liquid.
    Answer: weight
  14. The instrument used to find the density of a liquid is called a _______.
    Answer: density bottle
  15. The volume of a regular solid is calculated using its _______ dimensions.
    Answer: geometrical
  16. The relative density of pure water is taken as _______.
    Answer: 1
  17. The S.I. unit of mass is _______.
    Answer: kilogram
  18. The S.I. unit of volume is _______.
    Answer: cubic metre
  19. The density of water in S.I. unit is _______ kg/m³.
    Answer: 1000
  20. The density of gold is about _______ g/cm³.
    Answer: 19.3
  21. A submarine floats or sinks by controlling the _______ force.
    Answer: buoyant
  22. The relative density of kerosene is approximately _______.
    Answer: 0.8
  23. The density of iron is approximately _______ g/cm³.
    Answer: 7.8
  24. _______ is a device used to collect displaced water when measuring volume.
    Answer: Measuring cylinder
  25. An iron ship floats because its average density is _______ than that of water.
    Answer: less
  26. A floating body displaces an amount of liquid equal to its _______.
    Answer: weight
  27. The density of mercury is _______ g/cm³.
    Answer: 13.6
  28. The mass of 1 cm³ of water is _______ g.
    Answer: 1
  29. If a body floats partially submerged, its weight is _______ the buoyant force.
    Answer: equal to
  30. The volume of a liquid is commonly measured in _______.
    Answer: cm³ or mL
  31. The floating of ice in water is an example of the _______ of flotation.
    Answer: law
  32. In density bottle method, excess liquid escapes through the _______ in the stopper.
    Answer: hole
  33. If the relative density of a liquid is less than 1, it will _______ on water.
    Answer: float
  34. Volume of an object is the amount of _______ it occupies.
    Answer: space
  35. If a substance displaces more water, its volume is said to be _______.
    Answer: larger
  36. A density bottle has a _______ volume.
    Answer: fixed
  37. The density of air is about _______ kg/m³.
    Answer: 1.29
  38. When a body is fully immersed and floats, the weight of liquid displaced is _______ to its own weight.
    Answer: equal
  39. Relative density = density of substance ÷ density of _______.
    Answer: water
  40. The density of wood is _______ than 1 g/cm³.
    Answer: less
  41. A whale floats due to presence of _______ in its lungs.
    Answer: air
  42. A balloon rises because helium is _______ than air.
    Answer: lighter
  43. The term “float” means to remain _______ on the surface.
    Answer: suspended
  44. An object weighing more than the liquid it displaces will _______.
    Answer: sink
  45. Archimedes’ principle explains the concept of _______ force.
    Answer: buoyant
  46. The reading on a measuring cylinder is taken from the _______ of the meniscus.
    Answer: lower part
  47. 1 m³ = _______ cm³.
    Answer: 10⁶
  48. Measuring beakers are _______ accurate than measuring cylinders.
    Answer: less
  49. A substance with RD > 1 will _______ in water.
    Answer: sink
  50. The volume of displaced liquid is equal to the volume of the _______ solid.
    Answer: irregular

Name the Following

  1. Name the quantity defined as mass per unit volume.
    Answer: Density
  2. Name the instrument used to measure volume of an irregular solid.
    Answer: Eureka can
  3. Name the standard substance used for comparison in relative density.
    Answer: Water
  4. Name the S.I. unit of density.
    Answer: Kilogram per cubic metre (kg/m³)
  5. Name the C.G.S. unit of density.
    Answer: Gram per cubic centimetre (g/cm³)
  6. Name the principle on which the flotation of a body is based.
    Answer: Archimedes’ Principle
  7. Name the law which governs the condition for flotation.
    Answer: Law of flotation
  8. Name the liquid with density 13.6 g/cm³.
    Answer: Mercury
  9. Name the gas which is lighter than air and used in balloons.
    Answer: Helium
  10. Name the solid that floats in water due to low density.
    Answer: Ice
  11. Name the device used to find the density of liquids accurately.
    Answer: Density bottle
  12. Name the vessel used for approximate volume measurement in laboratory.
    Answer: Measuring beaker
  13. Name the vessel used for accurate measurement of liquids.
    Answer: Measuring cylinder
  14. Name the force that helps objects float in fluids.
    Answer: Buoyant force
  15. Name the type of solid whose volume is calculated using geometry.
    Answer: Regular solid
  16. Name the body that floats fully submerged in water.
    Answer: Body with density equal to water
  17. Name the physical quantity that has no unit in relative measurement.
    Answer: Relative density
  18. Name the force that acts opposite to the weight of a submerged object.
    Answer: Buoyant force
  19. Name the condition when weight of body equals upthrust.
    Answer: Floating
  20. Name the container from which displaced liquid flows out.
    Answer: Spout of Eureka can
  21. Name the part of the density bottle that allows excess liquid to escape.
    Answer: Fine hole in stopper
  22. Name the principle used in finding volume by displacement method.
    Answer: Archimedes’ Principle
  23. Name the state of matter with highest density.
    Answer: Solid
  24. Name the term for the amount of space occupied by a body.
    Answer: Volume
  25. Name the quantity that determines whether a body floats or sinks.
    Answer: Density
  26. Name the SI unit of mass.
    Answer: Kilogram (kg)
  27. Name the SI unit of volume.
    Answer: Cubic metre (m³)
  28. Name the quantity that remains unchanged when a body changes its state.
    Answer: Mass
  29. Name the body part of a whale that helps it float.
    Answer: Lungs
  30. Name the quantity obtained by dividing mass by volume.
    Answer: Density
  31. Name the physical quantity that is lighter in gases than in solids.
    Answer: Density
  32. Name one application of flotation used in warships.
    Answer: Submarine
  33. Name the unit used to measure volume of small amounts of liquids.
    Answer: Millilitre (mL)
  34. Name the property that enables wood to float on water.
    Answer: Low density
  35. Name the scientific term for rise of a body in a fluid.
    Answer: Buoyancy
  36. Name a metal that sinks in water due to high density.
    Answer: Iron
  37. Name the basic physical quantity used to define density.
    Answer: Mass
  38. Name the law which says that the weight of displaced liquid equals the weight of floating body.
    Answer: Law of flotation
  39. Name the measuring instrument that can have a parallax error.
    Answer: Measuring cylinder
  40. Name the form of water which has lesser density than liquid water.
    Answer: Ice
  41. Name the type of object that displaces its own weight of liquid.
    Answer: Floating object
  42. Name the process used to find density of an irregular object.
    Answer: Displacement method
  43. Name a household example where flotation is observed.
    Answer: Ice cubes in water
  44. Name the gas inside a submarine that helps it rise.
    Answer: Air
  45. Name the scientist who discovered the principle of buoyancy.
    Answer: Archimedes
  46. Name the method used to find the density of kerosene oil.
    Answer: Density bottle method
  47. Name the unit of relative density.
    Answer: No unit
  48. Name one factor that affects buoyant force.
    Answer: Density of liquid
  49. Name the effect responsible for rising of hot air balloons.
    Answer: Buoyancy
  50. Name the property of iron ship that helps it displace more water.
    Answer: Large volume

Answer in One Word

  1. What is the S.I. unit of density?
    Answer: kg/m³
  2. What is the C.G.S. unit of density?
    Answer: g/cm³
  3. Which force helps objects float in fluids?
    Answer: Buoyancy
  4. Which principle is used to explain flotation?
    Answer: Archimedes’
  5. Which solid naturally floats on water?
    Answer: Ice
  6. What is the unit of relative density?
    Answer: None
  7. What is the density of water in g/cm³?
    Answer: 1
  8. Which container is used to measure volume of an irregular object?
    Answer: Eureka can
  9. Which instrument is used to accurately measure liquid volume?
    Answer: Measuring cylinder
  10. Which instrument has a fixed volume and is used to determine density?
    Answer: Density bottle
  11. What kind of quantity is density: scalar or vector?
    Answer: Scalar
  12. What is the mass of 1 cm³ of water?
    Answer: 1 g
  13. Which gas is filled in balloons to make them float?
    Answer: Helium
  14. Which quantity determines if a body will sink or float?
    Answer: Density
  15. What is the value of 1 g/cm³ in kg/m³?
    Answer: 1000
  16. What is displaced by a floating body?
    Answer: Liquid
  17. What is the density of ice (approximate)?
    Answer: 0.92 g/cm³
  18. What is the S.I. unit of mass?
    Answer: Kilogram
  19. What is the S.I. unit of volume?
    Answer: Cubic metre
  20. What type of solid has measurable dimensions?
    Answer: Regular
  21. What type of solid has to be measured using displacement?
    Answer: Irregular
  22. What is the term for the ratio of density of a substance to water?
    Answer: Relative density
  23. What is the density of mercury in g/cm³?
    Answer: 13.6
  24. What is the density of gold in g/cm³?
    Answer: 19.3
  25. Which law states a floating body displaces its own weight of liquid?
    Answer: Flotation
  26. Which principle is used to find volume by displacement?
    Answer: Archimedes’
  27. What is the name of the part in the density bottle that allows overflow?
    Answer: Stopper
  28. What is the density of iron (approximate)?
    Answer: 7.8 g/cm³
  29. Which state of matter has highest density?
    Answer: Solid
  30. What happens to a body when its weight is less than buoyant force?
    Answer: Floats
  31. What quantity is measured in cubic centimetres?
    Answer: Volume
  32. Which term describes the upward force exerted by a fluid?
    Answer: Buoyancy
  33. What is used to measure volume of displaced liquid?
    Answer: Measuring cylinder
  34. What is the reading error called when eye is not level with scale?
    Answer: Parallax
  35. What is the term for an object that neither sinks nor rises in water?
    Answer: Suspended
  36. What kind of quantity is relative density?
    Answer: Ratio
  37. What does a floating object displace in a liquid?
    Answer: Weight
  38. What is the density of air (approximate) in kg/m³?
    Answer: 1.29
  39. What gas do whales use to float in water?
    Answer: Air
  40. What kind of motion causes a submarine to sink or rise?
    Answer: Buoyancy
  41. What force opposes the weight of a floating object?
    Answer: Upthrust
  42. What is the common unit of small liquid volumes?
    Answer: mL
  43. Which principle is the basis of the Eureka can method?
    Answer: Archimedes’
  44. What is the amount of matter in a body called?
    Answer: Mass
  45. What is the term for the space occupied by a body?
    Answer: Volume
  46. Which unit is used for density in C.G.S. system?
    Answer: g/cm³
  47. What is the name of the curved surface of a liquid in a cylinder?
    Answer: Meniscus
  48. What should be the eye level when reading a cylinder?
    Answer: Horizontal
  49. What happens when a body’s density is more than water?
    Answer: Sinks
  50. What happens when a body’s density equals that of water?
    Answer: Suspends

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Find the Odd One Out

  1. Ice, Iron, Wood, Gold
    Answer: Ice
    Explanation: Ice floats in water; others sink due to higher density.
  2. kg, g, mL, mg
    Answer: mL
    Explanation: mL is a unit of volume; others are units of mass.
  3. Density, Mass, Volume, Area
    Answer: Area
    Explanation: Area is 2D; others are physical quantities related to 3D space.
  4. Mercury, Water, Oil, Iron
    Answer: Iron
    Explanation: Iron is a solid; others are liquids.
  5. Eureka can, Beam balance, Density bottle, Measuring cylinder
    Answer: Beam balance
    Explanation: Beam balance measures mass; others measure volume.
  6. Kilogram, Cubic metre, Gram, Milligram
    Answer: Cubic metre
    Explanation: Cubic metre is a unit of volume; others are units of mass.
  7. Buoyancy, Density, Mass, Meniscus
    Answer: Meniscus
    Explanation: Meniscus is a surface phenomenon; others are physical quantities.
  8. Ice, Wax, Iron, Wood
    Answer: Iron
    Explanation: Iron sinks in water; others float.
  9. Gold, Mercury, Lead, Helium
    Answer: Helium
    Explanation: Helium is a gas; others are heavy metals.
  10. Archimedes’ principle, Pascal’s law, Law of flotation, Buoyancy
    Answer: Pascal’s law
    Explanation: Pascal’s law deals with pressure; others with flotation and fluids.
  11. Measuring beaker, Measuring cylinder, Density bottle, Stopwatch
    Answer: Stopwatch
    Explanation: Stopwatch measures time; others measure volume or density.
  12. Relative density, Density, Volume, Area
    Answer: Area
    Explanation: Area is 2D; others relate to 3D space or matter.
  13. Whale, Balloon, Ship, Spoon
    Answer: Spoon
    Explanation: Spoon does not float; others are examples of flotation.
  14. 1000 kg/m³, 1 g/cm³, 13.6 g/cm³, 1.29 kg/m³
    Answer: 13.6 g/cm³
    Explanation: It’s the density of mercury, much higher than others.
  15. Iceberg, Submarine, Rock, Ship
    Answer: Rock
    Explanation: Rock sinks; others float.
  16. Kilogram, Tonne, Metre, Gram
    Answer: Metre
    Explanation: Metre is a unit of length; others are units of mass.
  17. Density, Temperature, Volume, Mass
    Answer: Temperature
    Explanation: Temperature is not involved in calculating density directly.
  18. Air, Helium, Oxygen, Wood
    Answer: Wood
    Explanation: Wood is a solid; others are gases.
  19. Ice, Lead, Aluminium, Copper
    Answer: Ice
    Explanation: Ice floats; others sink.
  20. Archimedes, Newton, Pascal, Galileo
    Answer: Newton
    Explanation: Newton is not known for work on buoyancy or fluid principles.
  21. Eureka can, Thermometer, Measuring cylinder, Density bottle
    Answer: Thermometer
    Explanation: Thermometer measures temperature; others measure volume/density.
  22. Ship, Submarine, Balloon, Stone
    Answer: Stone
    Explanation: Stone sinks; others float.
  23. cm³, m³, g/cm³, mL
    Answer: g/cm³
    Explanation: g/cm³ is a unit of density; others are volume units.
  24. Gold, Mercury, Copper, Water
    Answer: Water
    Explanation: Water is not a metal; others are metals.
  25. Lungs, Blubber, Fins, Air
    Answer: Fins
    Explanation: Fins are for motion; others aid flotation.
  26. Archimedes’ principle, Law of flotation, Newton’s third law, Buoyancy
    Answer: Newton’s third law
    Explanation: Not related to flotation.
  27. 7.8 g/cm³, 1.0 g/cm³, 0.8 g/cm³, 19.3 g/cm³
    Answer: 19.3 g/cm³
    Explanation: Gold’s density is much higher than others.
  28. Parallax, Density, Volume, Mass
    Answer: Parallax
    Explanation: Parallax is an error, not a physical quantity.
  29. Eureka can, Overflow jar, Thermometer, Measuring cylinder
    Answer: Thermometer
    Explanation: Measures temperature, not volume.
  30. Kilogram, Gram, Newton, Milligram
    Answer: Newton
    Explanation: Newton is a unit of force; others are mass.
  31. Measuring tape, Measuring beaker, Measuring cylinder, Density bottle
    Answer: Measuring tape
    Explanation: Measures length, not volume.
  32. Relative density, Volume, Mass, Length
    Answer: Relative density
    Explanation: It has no unit; others do.
  33. Ice, Plastic, Iron, Wax
    Answer: Iron
    Explanation: Sinks in water; others float.
  34. Solid, Liquid, Gas, Force
    Answer: Force
    Explanation: Not a state of matter.
  35. Mercury, Gold, Kerosene, Lead
    Answer: Kerosene
    Explanation: It’s a liquid with low density; others are heavy.
  36. Ship, Iceberg, Submarine, Hammer
    Answer: Hammer
    Explanation: Does not float.
  37. cm, m, kg, mm
    Answer: kg
    Explanation: kg is mass unit; others are length.
  38. Water, Oil, Spirit, Iron
    Answer: Iron
    Explanation: Solid; others are liquids.
  39. g/cm³, kg/m³, kg, g
    Answer: kg
    Explanation: It’s a mass unit, not a density unit.
  40. Air, Ice, Gold, Wood
    Answer: Gold
    Explanation: It sinks; others float.
  41. Litre, m³, mL, kg
    Answer: kg
    Explanation: Mass unit; others are volume units.
  42. Buoyancy, Volume, Area, Density
    Answer: Area
    Explanation: Not involved in flotation.
  43. Spring balance, Beam balance, Measuring cylinder, Electronic balance
    Answer: Measuring cylinder
    Explanation: Measures volume; others measure mass.
  44. Density, Displacement, Temperature, Flotation
    Answer: Temperature
    Explanation: Not part of flotation calculation.
  45. mL, cm³, g, L
    Answer: g
    Explanation: Mass unit; others are volume.
  46. Rock, Iceberg, Air-filled balloon, Wood
    Answer: Rock
    Explanation: It sinks.
  47. Upthrust, Weight, Gravity, Surface tension
    Answer: Surface tension
    Explanation: Not involved in flotation.
  48. 0.8, 1.0, 1.2, 100
    Answer: 100
    Explanation: Not a typical relative density value.
  49. Float, Sink, Displace, Evaporate
    Answer: Evaporate
    Explanation: Not related to buoyancy or flotation.
  50. kg/m³, g/cm³, m/s, g/mL
    Answer: m/s
    Explanation: Unit of speed, not density.

Match the Pair

 Match the Pairs – Set 1

Column A

  1. Density
  2. Volume
  3. Eureka can
  4. Archimedes
  5. Density bottle

Column B

(a) Measures volume of irregular solids
 (b) Discovered buoyancy
 (c) Mass per unit volume
 (d) Fixed volume container
 (e) Space occupied by a body

Answer Key – Set 1
 1 → (c)
 2 → (e)
 3 → (a)
 4 → (b)
 5 → (d)

 Match the Pairs – Set 2

Column A

  1. Iron
  2. Mercury
  3. Helium
  4. Wood
  5. Ice

Column B

(a) Lighter than air
 (b) Sinks in water
 (c) Floats in water
 (d) Floats due to air pockets
 (e) Density = 13.6 g/cm³

Answer Key – Set 2
 1 → (b)
 2 → (e)
 3 → (a)
 4 → (d)
 5 → (c)

 Match the Pairs – Set 3

Column A

  1. Buoyant force
  2. Mass
  3. Measuring cylinder
  4. Relative density
  5. Measuring beaker

Column B

(a) Less accurate volume measure
 (b) Measured in grams
 (c) Upward force in fluids
 (d) No unit
 (e) Accurate volume measurement

Answer Key – Set 3
 1 → (c)
 2 → (b)
 3 → (e)
 4 → (d)
 5 → (a)

 Match the Pairs – Set 4

Column A

  1. Floating condition
  2. Law of flotation
  3. Water
  4. Density of gold
  5. Volume unit (S.I.)

Column B

(a) Displaces its own weight
 (b) 19.3 g/cm³
 (c) 1 g/cm³
 (d) Weight = buoyant force
 (e) m³

Answer Key – Set 4
 1 → (d)
 2 → (a)
 3 → (c)
 4 → (b)
 5 → (e)

 Match the Pairs – Set 5

Column A

  1. Upthrust
  2. Ship
  3. Whale
  4. Balloon
  5. Submarine

Column B

(a) Floats due to air in lungs
 (b) Can rise and sink
 (c) Floats due to average density
 (d) Buoyant force
 (e) Rises due to helium

Answer Key – Set 5
 1 → (d)
 2 → (c)
 3 → (a)
 4 → (e)
 5 → (b)

 Match the Pairs – Set 6

Column A

  1. g/cm³
  2. kg/m³
  3. g
  4. cm³
  5. 1 g/cm³

Column B

(a) Unit of mass
 (b) 1000 kg/m³
 (c) C.G.S. unit of density
 (d) S.I. unit of density
 (e) C.G.S. unit of volume

Answer Key – Set 6
 1 → (c)
 2 → (d)
 3 → (a)
 4 → (e)
 5 → (b)

 Match the Pairs – Set 7

Column A

  1. Iceberg
  2. Parallax error
  3. Meniscus
  4. Measuring scale
  5. Regular solid

Column B

(a) Floats with 1/10th above water
 (b) Lower curved surface
 (c) Causes reading mistake
 (d) Used for measuring length
 (e) Volume by formula

Answer Key – Set 7
 1 → (a)
 2 → (c)
 3 → (b)
 4 → (d)
 5 → (e)

 Match the Pairs – Set 8

Column A

  1. Ship made of iron
  2. Floating object
  3. Sinking object
  4. Litre
  5. Density of air

Column B

(a) Weight < buoyant force
 (b) 1.29 kg/m³
 (c) Large volume, low average density
 (d) Volume unit
 (e) Weight > buoyant force

Answer Key – Set 8
 1 → (c)
 2 → (a)
 3 → (e)
 4 → (d)
 5 → (b)

 Match the Pairs – Set 9

Column A

  1. Water displacement
  2. Volume of irregular solid
  3. Density of iron
  4. Relative density of oil
  5. Archimedes’ principle

Column B

(a) About 7.8 g/cm³
 (b) Measured using Eureka can
 (c) Explains buoyancy
 (d) About 0.8
 (e) Equal to object’s volume

Answer Key – Set 9
 1 → (e)
 2 → (b)
 3 → (a)
 4 → (d)
 5 → (c)

 Match the Pairs – Set 10

Column A

  1. Fixed volume
  2. Object floats
  3. Volume of water displaced
  4. Shape of iron ship
  5. Relative density of kerosene

Column B

(a) Less than object’s weight
 (b) Density bottle
 (c) Less than 1
 (d) Increases buoyancy
 (e) Equal to object’s weight

Answer Key – Set 10
 1 → (b)
 2 → (e)
 3 → (e)
 4 → (d)
 5 → (c)

Short Answer Questions  

  1. What is density?
    Answer: Density is the mass of a substance per unit volume.
  2. Write the formula for density.
    Answer: Density (ρ) = Mass (m) / Volume (V)
  3. Define relative density.
    Answer: Relative density is the ratio of the density of a substance to the density of water.
  4. What is the unit of relative density?
    Answer: Relative density has no unit.
  5. State the S.I. unit of density.
    Answer: Kilogram per cubic metre (kg/m³)
  6. What is the C.G.S. unit of density?
    Answer: Gram per cubic centimetre (g/cm³)
  7. How is the density of an irregular solid determined?
    Answer: By using a Eureka can to measure volume and a balance to measure mass.
  8. Name two vessels used to measure the volume of liquids.
    Answer: Measuring cylinder and measuring beaker.
  9. What is the density of pure water in g/cm³?
    Answer: 1 g/cm³
  10. What is the principle of flotation?
    Answer: A body floats if its weight is equal to the buoyant force.
  11. State the law of flotation.
    Answer: A floating body displaces its own weight of the liquid in which it floats.
  12. What does a density bottle measure?
    Answer: The density of liquids.
  13. Name the part of a density bottle that allows excess liquid to escape.
    Answer: The fine hole in the stopper.
  14. What is the density of gold?
    Answer: 19.3 g/cm³
  15. What happens when the relative density of a substance is greater than 1?
    Answer: The substance sinks in water.
  16. What is the average density of iron?
    Answer: 7.8 g/cm³
  17. Why does ice float on water?
    Answer: Because its density (0.92 g/cm³) is less than that of water.
  18. What causes buoyant force on an object?
    Answer: The upward pressure exerted by the liquid.
  19. Define volume.
    Answer: Volume is the amount of space occupied by a body.
  20. What is the S.I. unit of volume?
    Answer: Cubic metre (m³)
  21. What is the S.I. unit of mass?
    Answer: Kilogram (kg)
  22. Why does a balloon filled with helium rise in air?
    Answer: Because helium is lighter than air.
  23. What is the role of a Eureka can?
    Answer: It is used to measure the volume of an irregular solid by displacement.
  24. Why does an iron ship float on water?
    Answer: Because its average density is less than that of water.
  25. What is the density of mercury?
    Answer: 13.6 g/cm³
  26. Why is relative density a pure number?
    Answer: Because it is the ratio of two densities with the same units.
  27. Name a gas lighter than air.
    Answer: Helium
  28. Which state of matter generally has the highest density?
    Answer: Solid
  29. Which is more accurate: measuring cylinder or beaker?
    Answer: Measuring cylinder
  30. Why is oil used to demonstrate floating substances?
    Answer: Because it is less dense than water.
  31. What happens to the density of a substance if its volume increases but mass remains same?
    Answer: Density decreases.
  32. What is displaced when a body is immersed in a liquid?
    Answer: Volume of the liquid equal to the submerged volume of the body.
  33. What is the relative density of kerosene?
    Answer: Approximately 0.8
  34. What is the unit of density in the S.I. system?
    Answer: kg/m³
  35. What is the relation between 1 g/cm³ and kg/m³?
    Answer: 1 g/cm³ = 1000 kg/m³
  36. Name one factor that affects buoyant force.
    Answer: Density of the liquid
  37. Define mass.
    Answer: Mass is the amount of matter present in a body.
  38. What type of quantity is density – scalar or vector?
    Answer: Scalar
  39. Name one use of the density bottle.
    Answer: To determine the relative density of liquids.
  40. What is the density of air approximately?
    Answer: 1.29 kg/m³
  41. What is the formula for relative density using density bottle?
    Answer: (Mass of bottle + liquid – empty bottle) ÷ (Mass of bottle + water – empty bottle)
  42. What is the condition for a body to sink in a liquid?
    Answer: Its weight is greater than the buoyant force.
  43. What is the condition for a body to float just submerged?
    Answer: Its weight is equal to the buoyant force.
  44. Name a marine animal that floats due to air in its lungs.
    Answer: Whale
  45. Name the principle that explains why objects float.
    Answer: Archimedes’ principle
  46. What happens to a body when its density is less than that of water?
    Answer: It floats.
  47. What does the displaced water from Eureka can indicate?
    Answer: Volume of the object immersed.
  48. What is the purpose of the stopper with a hole in a density bottle?
    Answer: To allow overflow of excess liquid for accurate measurement.
  49. What is the volume of 1 litre in cm³?
    Answer: 1000 cm³
  50. What happens to density if both mass and volume are doubled?
    Answer: It remains unchanged.

Puzzles

  1. I tell how tightly matter is packed—two letters to start, ends with “ty.” What am I?
    Answer: Density
  2. I measure liquids by graduations on a cylinder—what vessel am I?
    Answer: Measuring cylinder
  3. Fill me with water and object to find its volume—I’m used in displacement—what am I?
    Answer: Eureka can
  4. Use me to find liquid density; I have a handy stoppered neck—what am I?
    Answer: Density bottle
  5. I’m the ratio of density to water—no units, just compare—what am I?
    Answer: Relative density
  6. I’m Sir ? Aristotle didn’t discover me, but Archimedes did—who am I?
    Answer: Archimedes
  7. I float when upthrust equals my weight—what am I demonstrating?
    Answer: Principle of flotation
  8. I’ve got kg/m³ for my unit—what quantity am I?
    Answer: Density (S.I. unit)
  9. I’m the C.G.S. cousin—g/cm³—what concept am I?
    Answer: Density
  10. I’m used to read the meniscus at eye level—what error do I prevent?
    Answer: Parallax error
  11. I’m 19.3 g/cm³—dense and heavy, I’m used in jewelry—what metal am I?
    Answer: Gold
  12. I occupy 1 cm³ and weigh 1 g—what substance am I?
    Answer: Water
  13. I float partly submerged—my weight equals buoyant force—what am I?
    Answer: Floating body
  14. I’m lowered weight using ballast tanks—what vessel am I?
    Answer: Submarine
  15. I sink in water but have a high density—not lighter air—what metal am I?
    Answer: Iron
  16. I displace water equal to my own weight—this is my law—what is it?
    Answer: Law of flotation
  17. I compare density to water, so water is my benchmark—what am I?
    Answer: Relative density
  18. I’m less dense than water so I float—brown bark, natural wood—what am I?
    Answer: Wood
  19. I’m used to calculate volume of cubes and spheres—what formula am I?
    Answer: Geometrical formula
  20. I rise when heated—used in balloons—what gas am I?
    Answer: Helium
  21. My density ~0.92 g/cm³, I float on ponds—what am I?
    Answer: Ice
  22. I’m measured in kg/m³ or g/cm³—what physical quantity am I?
    Answer: Density
  23. I hold water and overflow when an object is immersed—spout at side—what am I?
    Answer: Eureka can
  24. I’m the lost weight in water, equal to buoyant force—what am I?
    Answer: Upthrust
  25. I have a central hole in stopper and fixed volume—what am I?
    Answer: Density bottle
  26. I am less dense than water—floatable oil used in lamps—what am I?
    Answer: Kerosene
  27. I tell how much space you occupy—m³ or cm³ are my units—what am I?
    Answer: Volume
  28. I’m the density of water compared to water—always equal to 1—what am I?
    Answer: Relative density
  29. I float on water because I displace enough water equal to weight—what am I demonstrating?
    Answer: Principle of flotation
  30. I expand when freezing, so I float—what am I?
    Answer: Ice
  31. I help identify metals by measuring my ratio to water—what am I?
    Answer: Relative density
  32. I’m the upward force in water that lifts bodies—what am I?
    Answer: Buoyant force
  33. I’m identified by using Eureka can—what property am I measuring?
    Answer: Volume of irregular solid
  34. I weigh less when submerged in water—why?
    Answer: Buoyant force
  35. I’m the error prevented by reading the lower meniscus—what do I avoid?
    Answer: Parallax error
  36. I compare densities and have no units—what am I?
    Answer: Relative density
  37. I float because shape leads to low average density—what am I?
    Answer: Ship
  38. I displace my own weight of water to float—what principle is this?
    Answer: Law of flotation
  39. I have density ~13.6 g/cm³ and sink sharply—what liquid am I?
    Answer: Mercury
  40. I displace water equal to my volume, so I’m used to measure volume—what am I?
    Answer: Eureka can
  41. I rise in water if lighter than it—what term describes me?
    Answer: Floating
  42. I have kg/m³ as unit—derived from kg and m³—what am I?
    Answer: Density
  43. I’m the reader of cylinders—careful with curvature—what do I read?
    Answer: Meniscus
  44. I displace water—volume of object equals volume of displaced liquid—whose principle?
    Answer: Archimedes’ principle
  45. I occupy less space but weigh more than water—sink fast—what could I be?
    Answer: Lead
  46. I float with 90% below surface—largest piece in cold ocean—what am I?
    Answer: Iceberg
  47. I’m the ratio 0.8 measured for a bottle of oil—what is this?
    Answer: Relative density of oil
  48. I can rise or sink by filling water tanks—amphibious vessel—what am I?
    Answer: Submarine
  49. I float due to filling with hot light air—what am I?
    Answer: Hot‑air balloon
  50. I have identical mass in air or water—what quantity am I?
    Answer: Mass

Difference Between:

  1. Difference between Mass and Weight
    Answer:
    Mass is the quantity of matter in a body and remains constant everywhere.
     Weight is the force with which Earth attracts a body and varies with gravity.
  2. Difference between Density and Relative Density
    Answer:
    Density is mass per unit volume of a substance, expressed in g/cm³ or kg/m³.
     Relative density is the ratio of the density of a substance to the density of water and has no unit.
  3. Difference between Volume and Density
    Answer:
    Volume is the amount of space occupied by a body, measured in cm³ or m³.
     Density is the mass per unit volume of a body, measured in g/cm³ or kg/m³.
  4. Difference between Regular Solid and Irregular Solid
    Answer:
    A regular solid has fixed shape and measurable dimensions, so its volume can be calculated using formulae.
     An irregular solid has uneven shape and its volume is measured by displacement method.
  5. Difference between C.G.S. and S.I. Units of Density
    Answer:
    C.G.S. unit of density is g/cm³.
     S.I. unit of density is kg/m³.
  6. Difference between Measuring Cylinder and Measuring Beaker
    Answer:
    Measuring cylinder is tall and narrow, giving more accurate readings.
     Measuring beaker is wide and has fewer graduation marks, less accurate.
  7. Difference between Measuring Cylinder and Eureka Can
    Answer:
    Measuring cylinder is used to directly measure volume of liquids.
     Eureka can is used to measure volume of irregular solids by displacement.
  8. Difference between Weight in Air and Weight in Water
    Answer:
    Weight in air is the actual weight of the body.
     Weight in water appears less due to the buoyant force acting upwards.
  9. Difference between Floatation and Sinking
    Answer:
    Floatation occurs when the upthrust equals or exceeds the weight of the body.
     Sinking occurs when the weight of the body exceeds the upthrust.
  10. Difference between Law of Floatation and Archimedes’ Principle
    Answer:
    Law of floatation states that a floating body displaces its own weight of the liquid.
     Archimedes’ principle states that a body immersed in liquid experiences an upthrust equal to the weight of liquid displaced.
  11. Difference between Buoyant Force and Weight
    Answer:
    Buoyant force is the upward force exerted by a liquid on a body immersed in it.
     Weight is the downward force due to gravity on the body.
  12. Difference between Parallax Error and Instrumental Error
    Answer:
    Parallax error occurs due to incorrect eye-level reading.
     Instrumental error arises due to faults in the measuring instrument itself.
  13. Difference between Hot Air Balloon and Helium Balloon
    Answer:
    Hot air balloon rises due to hot air being lighter than surrounding air.
     Helium balloon rises because helium gas is lighter than air.
  14. Difference between Solid State and Liquid State (in context of density)
    Answer:
    Solids have high density due to closely packed molecules.
     Liquids have lower density as molecules are loosely packed.
  15. Difference between Sinking and Submerging
    Answer:
    Sinking means the body goes to the bottom as its weight > upthrust.
     Submerging means body is completely underwater, but not necessarily sinking.
  16. Difference between Meniscus and Parallax
    Answer:
    Meniscus is the curved surface of a liquid in a vessel.
     Parallax is the error observed when the eye is not at the level of the meniscus.
  17. Difference between Measuring Cylinder and Density Bottle
    Answer:
    Measuring cylinder is used to measure varying volumes of liquid.
     Density bottle has a fixed volume and is used to determine density.
  18. Difference between Displacement Method and Direct Volume Measurement
    Answer:
    Displacement method is used for irregular solids by measuring displaced liquid.
     Direct measurement is used for liquids and regular solids using measuring instruments.
  19. Difference between Accuracy and Precision
    Answer:
    Accuracy refers to how close a measurement is to the true value.
     Precision refers to how consistently close repeated measurements are to each other.
  20. Difference between Ice and Water (in terms of density)
    Answer:
    Ice has lower density (0.92 g/cm³), which is why it floats.
     Water has higher density (1 g/cm³), hence stays below ice.

Assertion and Reason

Instructions for answering:

Choose the correct option:

(A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

(C) Assertion is true, but Reason is false.

(D) Assertion is false, but Reason is true.


  1. Assertion: Ice floats on water.
    Reason: Ice has more density than water.
     Answer: (C)
     Explanation: Ice has lower density, not more.

  2. Assertion: Relative density is a pure number.
    Reason: Relative density is the ratio of two quantities having the same units.
     Answer: (A)
     Explanation: Units cancel, making it a pure number.

  3. Assertion: A stone sinks in water.
    Reason: The buoyant force on the stone is greater than its weight.
     Answer: (C)
     Explanation: Stone sinks when weight > buoyant force.

  4. Assertion: A balloon filled with helium rises in air.
    Reason: Helium is lighter than air.
     Answer: (A)
     Explanation: Both are true and directly related.

  5. Assertion: An iron ship floats on water.
    Reason: Iron is lighter than water.
     Answer: (C)
     Explanation: Iron is heavier, but ship’s average density is less.

  6. Assertion: Density of a substance depends on its mass and volume.
    Reason: Density is the product of mass and volume.
     Answer: (C)
     Explanation: Density = mass ÷ volume, not product.

  7. Assertion: Water has a relative density of 1.
    Reason: Water is used as the standard for comparison in relative density.
     Answer: (A)
     Explanation: Both are correct and related.

  8. Assertion: A body displaces liquid when immersed.
    Reason: Every solid occupies space in liquid.
     Answer: (A)
     Explanation: Immersion causes displacement due to volume.

  9. Assertion: A gold coin sinks in water.
    Reason: Gold has a density greater than water.
     Answer: (A)
     Explanation: Gold’s high density causes it to sink.

  10. Assertion: A floating body displaces liquid equal to its weight.
    Reason: This is explained by the law of flotation.
     Answer: (A)
     Explanation: Both are true and correctly linked.

  11. Assertion: Measuring cylinder is more accurate than measuring beaker.
    Reason: Measuring cylinders have finer graduations.
     Answer: (A)
     Explanation: Both are true and related.

  12. Assertion: Mass and weight of an object are always equal.
    Reason: Both are measured in kilograms.
     Answer: (D)
     Explanation: Mass and weight differ; weight is a force.

  13. Assertion: Relative density has no unit.
    Reason: It is the ratio of two densities with the same unit.
     Answer: (A)
     Explanation: Units cancel out.

  14. Assertion: Wood floats on water.
    Reason: Wood has higher density than water.
     Answer: (C)
     Explanation: It floats because it has lower density.

  15. Assertion: Mercury sinks in water.
    Reason: Mercury has more density than water.
     Answer: (A)
     Explanation: High density makes it sink.

  16. Assertion: Volume is a scalar quantity.
    Reason: It has magnitude but no direction.
     Answer: (A)
     Explanation: Correct definition of scalar.

  17. Assertion: Iron block sinks in water.
    Reason: Buoyant force on iron is greater than its weight.
     Answer: (C)
     Explanation: It sinks when weight > buoyant force.

  18. Assertion: Oil floats on water.
    Reason: Oil has less density than water.
     Answer: (A)
     Explanation: Low density allows it to float.

  19. Assertion: Volume of a liquid is measured in grams.
    Reason: Volume and mass have the same units.
     Answer: (D)
     Explanation: Volume is in cm³ or mL, not grams.

  20. Assertion: Eureka can is used to find volume of irregular solids.
    Reason: It collects the displaced water equal to the object’s volume.
     Answer: (A)
     Explanation: Correct tool and method.

  21. Assertion: Temperature affects density.
    Reason: Heating increases mass of a substance.
     Answer: (C)
     Explanation: Mass remains same; volume increases.

  22. Assertion: A body partially immersed in water is in equilibrium.
    Reason: Its weight equals the upthrust.
     Answer: (A)
     Explanation: This is the condition for floating.

  23. Assertion: A fully submerged object displaces less water.
    Reason: Displacement depends on volume of the body.
     Answer: (C)
     Explanation: Fully submerged displaces more water.

  24. Assertion: Gases have lower density than liquids.
    Reason: Molecules in gases are more spread out.
     Answer: (A)
     Explanation: Correct physical explanation.

  25. Assertion: Upthrust is also called buoyant force.
    Reason: It acts opposite to the direction of gravity.
     Answer: (A)
     Explanation: Both statements are correct.

  26. Assertion: A litre is equal to 1000 cm³.
    Reason: 1 mL = 1 cm³.
     Answer: (A)
     Explanation: Unit conversion is accurate.

  27. Assertion: Relative density of oil is 1.1.
    Reason: Oil floats on water.
     Answer: (D)
     Explanation: Oil has RD < 1, so value is incorrect.

  28. Assertion: Measuring cylinder measures length.
    Reason: It has a scale printed on it.
     Answer: (D)
     Explanation: It measures volume, not length.

  29. Assertion: Air has density.
    Reason: Air has both mass and volume.
     Answer: (A)
     Explanation: Satisfies density definition.

  30. Assertion: Water is denser than oil.
    Reason: Water has more mass per unit volume.
     Answer: (A)
     Explanation: Density = mass/volume.

  31. Assertion: Density = Volume ÷ Mass.
    Reason: It gives the amount of volume per unit mass.
     Answer: (D)
     Explanation: Formula is reversed; mass ÷ volume.

  32. Assertion: A body with RD = 1 floats on water.
    Reason: It displaces less water than its weight.
     Answer: (C)
     Explanation: It displaces equal to its weight.

  33. Assertion: Oil displaces more water than iron.
    Reason: Oil has less mass.
     Answer: (C)
     Explanation: Displacement depends on volume, not just mass.

  34. Assertion: A submarine can float or sink.
    Reason: It adjusts its density by controlling internal water.
     Answer: (A)
     Explanation: True and well explained.

  35. Assertion: Mercury is lighter than water.
    Reason: Mercury has low density.
     Answer: (D)
     Explanation: Mercury is heavier and denser.

  36. Assertion: Lighter objects always float.
    Reason: Floating depends only on mass.
     Answer: (D)
     Explanation: Depends on density, not just mass.

  37. Assertion: Buoyant force increases with depth.
    Reason: Pressure increases with depth.
     Answer: (A)
     Explanation: Both are true and related.

  38. Assertion: Units of relative density are g/cm³.
    Reason: It is the ratio of densities.
     Answer: (C)
     Explanation: It has no units.

  39. Assertion: Iron rod and ship both are made of iron.
    Reason: Ship floats because of its shape and hollow design.
     Answer: (A)
     Explanation: Shape affects average density.

  40. Assertion: A body floats if its weight equals buoyant force.
    Reason: Then, net force acting on body is zero.
     Answer: (A)
     Explanation: Zero net force leads to equilibrium.

  41. Assertion: 1 cm³ = 1 mL.
    Reason: Both measure volume.
     Answer: (A)
     Explanation: Correct unit equivalence.

  42. Assertion: Iron sinks in kerosene.
    Reason: Iron has higher density than kerosene.
     Answer: (A)
     Explanation: True and directly related.

  43. Assertion: Displacement method is not used for regular solids.
    Reason: Volume can be found using formula.
     Answer: (A)
     Explanation: Both are true and linked.

  44. Assertion: Parallax error occurs in digital balance.
    Reason: Eye position affects digital reading.
     Answer: (D)
     Explanation: Parallax occurs only in analog instruments.

  45. Assertion: More the density, more the mass.
    Reason: Density is independent of volume.
     Answer: (C)
     Explanation: Density = mass ÷ volume; not independent.

  46. Assertion: A hollow iron ball can float.
    Reason: Its average density can be less than water.
     Answer: (A)
     Explanation: Both correct and related.

  47. Assertion: Displaced volume equals volume of submerged part.
    Reason: Liquid is incompressible.
     Answer: (B)
     Explanation: Both are true, but not directly linked.

  48. Assertion: Density increases with increasing mass.
    Reason: Volume remains constant.
     Answer: (A)
     Explanation: Valid only if volume is unchanged.

  49. Assertion: Oil and petrol float on water.
    Reason: They have lower density than water.
     Answer: (A)
     Explanation: Both are lighter and float.

  50. Assertion: Density of a substance changes with temperature.
    Reason: Volume expands with temperature increase.
     Answer: (A)
     Explanation: Expansion reduces density.

True or False

  1. Density is defined as mass divided by volume.
    Answer: True
  2. Relative density has a unit.
    Answer: False
  3. The S.I. unit of volume is cubic metre.
    Answer: True
  4. Eureka can is used to measure the mass of irregular solids.
    Answer: False
  5. A body floats if its density is more than the liquid.
    Answer: False
  6. 1 g/cm³ is equal to 1000 kg/m³.
    Answer: True
  7. Measuring cylinder is used to find the temperature of a liquid.
    Answer: False
  8. Archimedes’ principle is used to determine the density of an irregular solid.
    Answer: True
  9. Wood sinks in water because its density is higher than water.
    Answer: False
  10. Density of ice is more than that of water.
    Answer: False
  11. Iron is denser than water and therefore sinks in it.
    Answer: True
  12. Relative density of water is taken as 1.
    Answer: True
  13. The volume of a cube is found using the displacement method.
    Answer: False
  14. A density bottle is used to find the density of liquids.
    Answer: True
  15. An object sinks in a liquid if its weight is more than the buoyant force.
    Answer: True
  16. A floating body displaces a volume of liquid equal to its own volume.
    Answer: False
  17. Oil floats on water because it is denser than water.
    Answer: False
  18. Measuring beaker is more accurate than measuring cylinder.
    Answer: False
  19. The principle of flotation is based on Archimedes’ principle.
    Answer: True
  20. Submarines control their flotation using ballast tanks.
    Answer: True
  21. The density of gold is less than the density of water.
    Answer: False
  22. 1 litre is equal to 1000 cm³.
    Answer: True
  23. The relative density of kerosene is about 1.2.
    Answer: False
  24. The density of mercury is approximately 13.6 g/cm³.
    Answer: True
  25. A balloon rises in air because helium is lighter than air.
    Answer: True
  26. Volume is measured in grams.
    Answer: False
  27. Parallax error can occur when reading a measuring cylinder.
    Answer: True
  28. A floating body displaces its own weight of the liquid.
    Answer: True
  29. Water is used as a reference substance to define relative density.
    Answer: True
  30. Density increases when volume increases and mass remains the same.
    Answer: False
  31. The S.I. unit of mass is gram.
    Answer: False
  32. A block of wood will float in water.
    Answer: True
  33. Ice has a relative density of 1.
    Answer: False
  34. The buoyant force acts in the downward direction.
    Answer: False
  35. Buoyant force increases with depth.
    Answer: True
  36. A measuring cylinder is used to measure force.
    Answer: False
  37. The volume of a liquid can be measured using a measuring cylinder.
    Answer: True
  38. The density of air is more than that of water.
    Answer: False
  39. The mass of an object changes when it is taken to the Moon.
    Answer: False
  40. The density of a substance is affected by temperature.
    Answer: True
  41. Gold sinks in water due to its low density.
    Answer: False
  42. The principle of flotation is not applicable to gases.
    Answer: False
  43. Volume of an irregular solid can be found using a Eureka can.
    Answer: True
  44. When an object floats, its weight is balanced by buoyant force.
    Answer: True
  45. A whale floats in water due to presence of iron in its body.
    Answer: False
  46. A floating object displaces more liquid than a sinking object.
    Answer: False
  47. Volume and mass have the same units.
    Answer: False
  48. Density is a scalar quantity.
    Answer: True
  49. Density of a substance remains the same in all states.
    Answer: False
  50. Air has both mass and volume, so it has density.
    Answer: True

Long Answer Questions

  1. Define density and write its unit in S.I. and C.G.S. systems.
    Answer:
    Density is defined as the mass of a substance per unit volume. It tells us how much matter is packed into a given volume.
     S.I. unit of density: kilogram per cubic metre (kg/m³)
     C.G.S. unit of density: gram per cubic centimetre (g/cm³)
  2. Define relative density. Why is it a unitless quantity?
    Answer:
    Relative density is the ratio of the density of a substance to the density of water. It is a unitless quantity because both the numerator and denominator have the same units, which cancel out.
     Relative Density = Density of substance / Density of water
  3. What is the principle of flotation? Explain with a condition for floating.
    Answer:
    The principle of flotation states that a body floats in a liquid if the weight of the body is equal to the buoyant force acting on it. If the weight is less than the buoyant force, the body floats. If it is more, the body sinks.
  4. State the law of flotation.
    Answer:
    The law of flotation states:
     A floating body displaces its own weight of the liquid in which it floats.
     This means that the weight of the liquid displaced is equal to the weight of the floating body.
  5. State Archimedes’ principle.
    Answer:
    Archimedes’ Principle states that when a body is fully or partially immersed in a liquid, it experiences an upward force equal to the weight of the liquid displaced by it. This upward force is called buoyant force or upthrust.
  6. What are the conditions under which a body floats or sinks in a liquid?
    Answer:
  • If the weight of the body is greater than the buoyant force, the body sinks.
  • If the weight is equal to the buoyant force, the body floats just submerged.
  • If the weight is less than the buoyant force, the body floats partially above the surface.
  1. Describe an experiment to find the density of a regular solid.
    Answer:
    To find the density:
  1. Measure the mass using a beam balance.
  2. Measure the volume using geometric formula (e.g., l × b × h for a cuboid).
  3. Use the formula: Density = Mass / Volume
  1. Describe how the density of an irregular solid is determined using a Eureka can.
    Answer:
  1. Measure the mass using a balance.
  2. Fill the Eureka can till water starts flowing out of its spout.
  3. Place a measuring cylinder below the spout.
  4. Gently immerse the object fully.
  5. Measure the volume of water collected (equal to object’s volume).
  6. Calculate density using: Density = Mass / Volume
  1. How can you find the density of a liquid using a density bottle?
    Answer:
  1. Measure the mass of the empty bottle (M₁).
  2. Fill it with water and weigh (M₂).
  3. Fill it with liquid and weigh (M₃).
  4. Volume of bottle = M₂ – M₁
  5. Mass of liquid = M₃ – M₁
  6. Density = (M₃ – M₁) / (M₂ – M₁)
  1. How does a ship made of iron float, though iron is denser than water?
    Answer:
    Although iron is denser than water, a ship is designed to displace a large volume of water. This increases the upthrust acting on it. The overall average density of the ship (including air-filled spaces) becomes less than that of water, enabling it to float.
  2. Why does an iron ball sink while a wooden block floats on water?
    Answer:
    An iron ball has density greater than water, so it displaces less water than its weight, and it sinks. A wooden block has lower density than water, so it displaces more water and receives enough upthrust to float.
  3. What is meant by buoyant force? On what factors does it depend?
    Answer:
    Buoyant force is the upward force experienced by a body when it is immersed in a fluid.
     It depends on:
  • Volume of the object submerged
  • Density of the fluid
  • Acceleration due to gravity
  1. State the differences between mass and weight.
    Answer:
  • Mass is the amount of matter in a body; weight is the force with which Earth attracts it.
  • Mass is constant; weight varies with gravity.
  • Mass is measured in kg; weight in newtons.
  • Mass is scalar; weight is vector.
  1. What precautions must be taken while using a measuring cylinder?
    Answer:
  • Place the cylinder on a flat surface.
  • Avoid parallax error by keeping eyes level with the meniscus.
  • Take the reading from the bottom of the meniscus.
  • Avoid spillage or tilting of the cylinder.
  1. Explain the construction and working of a density bottle.
    Answer:
    A density bottle is a small glass bottle of known volume with a tight-fitting stopper having a fine hole. When filled, excess liquid escapes through the hole ensuring exact volume. The mass of liquid inside is weighed to calculate density using known volume.
  2. A substance has mass 250 g and volume 50 cm³. Find its density.
    Answer:
    Given:
     Mass = 250 g
     Volume = 50 cm³
     Density = Mass / Volume = 250 / 50 = 5 g/cm³
  3. A block has density 7.5 g/cm³ and volume 8 cm³. Find its mass.
    Answer:
    Mass = Density × Volume = 7.5 × 8 = 60 g
  4. What is the relative density of a substance with density 0.8 g/cm³?
    Answer:
    Relative density = 0.8 / 1 = 0.8 (no unit)
  5. What is meant by volume? State its S.I. unit and common measuring instruments.
    Answer:
    Volume is the space occupied by a body.
     S.I. unit: m³
     Measured using:
  • Measuring cylinder
  • Measuring beaker
  • Eureka can (for irregular solids)
  1. What is the importance of meniscus in liquid measurements?
    Answer:
    The meniscus is the curved surface of a liquid. In measurements, reading is taken at the lower meniscus (for water-like liquids) to avoid errors. Accurate eye-level reading prevents parallax error.
  2. State the formula and units for density in both S.I. and C.G.S. systems.
    Answer:
    Formula: Density = Mass / Volume
     S.I. unit: kg/m³
     C.G.S. unit: g/cm³
  3. Why does a balloon rise in air when filled with helium?
    Answer:
    Helium is lighter than air, so the balloon has a lower average density. It displaces more weight of air than its own weight, resulting in an upward buoyant force which makes it rise.
  4. What causes a body to float partially in a liquid? Give example.
    Answer:
    When the weight of a body is less than the buoyant force, it floats partially submerged. Example: Iceberg floating in the ocean.
  5. Define and differentiate S.I. and C.G.S. units with example of density.
    Answer:
    S.I. units are based on the metric system using metre, kilogram, second.
     C.G.S. uses centimetre, gram, second.
     Example:
     Density in S.I. → kg/m³
     Density in C.G.S. → g/cm³
  6. Explain how a submarine controls its buoyancy.
    Answer:
    A submarine has ballast tanks which can be filled with water to increase density (to sink) or filled with air to decrease density (to float). This controls buoyancy based on Archimedes’ principle.
  7. A piece of wood floats on water while a piece of iron of the same size sinks. Why?
    Answer:
    Wood has lower density than water, so it experiences a greater upthrust than its weight and floats.
     Iron, being denser, has more weight than the upthrust and thus sinks.
  8. Why does ice float on water and not sink?
    Answer:
    Ice has a density of about 0.92 g/cm³, which is less than that of water (1 g/cm³). Hence, ice displaces its own weight of water before being fully submerged and floats.
  9. What is the role of a Eureka can in determining volume?
    Answer:
    A Eureka can helps measure the volume of an irregular solid by displacement method. The volume of water displaced equals the volume of the object when fully immersed.
  10. Describe how you can use displacement method to measure volume of a stone.
    Answer:
  • Fill a Eureka can until water just starts to flow out.
  • Place a measuring cylinder below the spout.
  • Gently lower the stone into the can.
  • Collect and measure the displaced water.
  • The volume of water displaced = volume of stone.
  1. A density bottle weighs 40 g when empty, 90 g when filled with water, and 80 g when filled with a liquid. Find the density of the liquid.
    Answer:
    Mass of water = 90 g – 40 g = 50 g
     Mass of liquid = 80 g – 40 g = 40 g
     Density of liquid = (Mass of liquid / Mass of water) × 1 g/cm³ = (40/50) × 1 = 0.8 g/cm³
  2. Why does a person feel lighter when swimming?
    Answer:
    In water, a person experiences an upward buoyant force equal to the weight of the water displaced. This counteracts their actual weight, making them feel lighter.
  3. Explain with an example how average density affects flotation.
    Answer:
    An iron ship floats because its hollow design increases volume and reduces average density below that of water. Despite being made of dense material, it floats due to lower average density.
  4. List three applications of flotation in daily life.
    Answer:
  1. Ice floats on water in cold regions.
  2. Life jackets help swimmers float.
  3. Ships and submarines use flotation principles for movement in water.
  1. A block of wood has volume 100 cm³ and mass 70 g. Find its density and state if it floats or sinks in water.
    Answer:
    Density = 70 g / 100 cm³ = 0.7 g/cm³
     Since 0.7 < 1, it floats in water.
  2. A body of volume 20 cm³ weighs 40 g in air and 20 g in water. Find upthrust and density of the body.
    Answer:
    Upthrust = Loss in weight = 40 g – 20 g = 20 g
     Volume = 20 cm³
     Density = Mass / Volume = 40 g / 20 cm³ = 2 g/cm³
  3. Explain why whales and other sea mammals can float easily.
    Answer:
    Whales have air in their lungs and blubber (fat) under their skin, both of which reduce their average density. As a result, they float easily due to upthrust.
  4. What is the density of air? Why is it lower than that of liquids and solids?
    Answer:
    The density of air is approximately 1.29 kg/m³.
     Air molecules are far apart compared to solids and liquids, resulting in much lower density.
  5. Give two advantages of using a density bottle over other volume measuring instruments.
    Answer:
  1. It provides fixed, accurate volume for comparison.
  2. It avoids reading/parallax errors common in graduated vessels.
  1. What is the significance of relative density in identifying substances?
    Answer:
    Each material has a characteristic relative density. Comparing measured relative density with standard values helps identify unknown substances.
  2. How do hot air balloons rise in air?
    Answer:
    Hot air is less dense than cold air. Heating air inside the balloon lowers its density, and the upthrust from the surrounding cooler, denser air lifts the balloon.
  3. A solid of mass 200 g and volume 250 cm³ is immersed in water. Will it float or sink? Justify.
    Answer:
    Density = 200/250 = 0.8 g/cm³
     Since 0.8 < 1, the solid floats in water.
  4. Why does an iron needle sink while an iron ship floats?
    Answer:
    An iron needle has high density and small volume, so it sinks. A ship has large volume with air spaces, reducing its average density and allowing it to float.
  5. Define and explain the term “parallax error.” How can it be avoided?
    Answer:
    Parallax error occurs when measurements are taken from an angle instead of eye-level. It can be avoided by aligning the eye with the lower meniscus of the liquid.
  6. Why is the density of solids usually higher than that of liquids or gases?
    Answer:
    In solids, molecules are tightly packed with minimal spaces, making mass per unit volume high. In gases, molecules are far apart, hence low density.
  7. Describe an activity to demonstrate the law of flotation.
    Answer:
    Float a wooden block in water. Collect displaced water in a beaker and weigh it. Weigh the wooden block separately. The two weights are approximately equal, verifying the law of flotation.
  8. Write the steps to calculate the relative density of a liquid using a density bottle.
    Answer:
  1. Weigh empty bottle (M₁).
  2. Fill with water and weigh (M₂).
  3. Fill with liquid and weigh (M₃).
  4. Relative Density = (M₃ – M₁) / (M₂ – M₁)
  1. Why does the reading of water level rise when an object is immersed in it?
    Answer:
    The object displaces water equal to its volume. This displaced water occupies space, causing the water level to rise.
  2. A body floats with 1/4 of its volume above water. What is its relative density?
    Answer:
    Fraction submerged = 3/4
     Relative density = 3/4 = 0.75
  3. A body of weight 50 N displaces water weighing 40 N. Will it float or sink?
    Answer:
    Weight > Buoyant force → 50 N > 40 N
     It will sink.
  4. Why does ice occupy more volume than water for the same mass?
    Answer:
    In ice, water molecules arrange in a crystal lattice with more space between them than in liquid water. Thus, ice has lower density and occupies more volume for the same mass.

Give Reasons

  1. Give reason: A wooden block floats on water.
    Answer: Because its density is less than that of water.
  2. Give reason: Iron sinks in water.
    Answer: Because its density is greater than that of water.
  3. Give reason: Ice floats on water.
    Answer: Because the density of ice (0.92 g/cm³) is less than that of water (1 g/cm³).
  4. Give reason: Density is a scalar quantity.
    Answer: Because it has only magnitude and no direction.
  5. Give reason: Relative density has no unit.
    Answer: Because it is the ratio of two densities having the same unit, which cancel out.
  6. Give reason: Ships float in water despite being made of iron.
    Answer: Because their average density is less than that of water due to their hollow design.
  7. Give reason: A balloon filled with helium rises in air.
    Answer: Because helium is lighter than air and its density is lower than that of air.
  8. Give reason: A submarine can rise and sink in water.
    Answer: Because it controls its buoyancy by filling or emptying ballast tanks.
  9. Give reason: A person feels lighter while swimming.
    Answer: Because the buoyant force of water acts upward against the person’s weight.
  10. Give reason: Gold sinks in water.
    Answer: Because its density is much higher than that of water.
  11. Give reason: Mercury is used in thermometers.
    Answer: Because it has high density and uniform expansion.
  12. Give reason: Air has density.
    Answer: Because it has both mass and volume.
  13. Give reason: Density bottle has a hole in the stopper.
    Answer: To allow excess liquid to escape and ensure accurate volume.
  14. Give reason: Parallax error occurs while reading a measuring cylinder.
    Answer: Because the eye is not placed at the level of the lower meniscus.
  15. Give reason: Relative density of a floating body is less than 1.
    Answer: Because its density is less than the density of water.
  16. Give reason: Measuring cylinder gives accurate volume.
    Answer: Because it has graduated markings for precise measurement.
  17. Give reason: Oil floats on water.
    Answer: Because its density is less than the density of water.
  18. Give reason: Measuring beaker is less accurate than measuring cylinder.
    Answer: Because it has wider diameter and fewer markings.
  19. Give reason: Eureka can is used to measure volume of irregular solids.
    Answer: Because it helps measure displaced water equal to the object’s volume.
  20. Give reason: The unit of density in S.I. is kg/m³.
    Answer: Because it is derived from mass in kg and volume in m³.
  21. Give reason: Floating bodies displace water.
    Answer: To balance their weight with the upthrust.
  22. Give reason: Icebergs float with most of their volume submerged.
    Answer: Because their density is slightly less than that of sea water.
  23. Give reason: A body sinks when its weight is more than the upthrust.
    Answer: Because the net force acts downward, making it sink.
  24. Give reason: Archimedes’ principle is used to find density of irregular solids.
    Answer: Because it helps determine the volume displaced by the object.
  25. Give reason: Balloons filled with hot air rise.
    Answer: Because hot air is less dense than cold air.
  26. Give reason: Ice occupies more volume than water.
    Answer: Because of the open structure of ice crystals, which increases volume.
  27. Give reason: A life jacket helps in floating.
    Answer: Because it increases the effective volume and decreases overall density.
  28. Give reason: Gases have low density.
    Answer: Because their molecules are widely spaced with less mass per unit volume.
  29. Give reason: Iron needle sinks in water.
    Answer: Because its small volume doesn’t displace enough water to support its weight.
  30. Give reason: We use lower meniscus to take liquid readings.
    Answer: Because it gives the most accurate measurement of the liquid level.
  31. Give reason: Water is used as a standard for relative density.
    Answer: Because it has a known density of 1 g/cm³ at 4°C.
  32. Give reason: Solids usually have higher density than liquids.
    Answer: Because their molecules are tightly packed with more mass per volume.
  33. Give reason: Volume is measured in m³ in the S.I. system.
    Answer: Because it’s the cube of the S.I. unit of length (metre).
  34. Give reason: Weight differs from place to place, but mass doesn’t.
    Answer: Because weight depends on gravity which varies, but mass is constant.
  35. Give reason: An iron ball and a wooden ball of same size behave differently in water.
    Answer: Because iron has higher density and sinks, while wood has lower density and floats.
  36. Give reason: Density increases if mass increases and volume remains constant.
    Answer: Because density is directly proportional to mass.
  37. Give reason: Density is important in material identification.
    Answer: Because each substance has a unique density value.
  38. Give reason: A body floats when its relative density is less than 1.
    Answer: Because it means the body is less dense than water.
  39. Give reason: Submarines adjust their depth using ballast tanks.
    Answer: To change their density and thus control buoyancy.
  40. Give reason: A cube’s volume can be calculated using formula.
    Answer: Because it is a regular solid with known dimensions.
  41. Give reason: A measuring scale cannot measure volume directly.
    Answer: Because it only measures length, not three-dimensional space.
  42. Give reason: Gases can rise in atmosphere.
    Answer: Because lighter gases displace heavier air and rise due to buoyancy.
  43. Give reason: Ships are hollow from inside.
    Answer: To reduce their average density and help them float.
  44. Give reason: Water overflows when an object is immersed.
    Answer: Because the object displaces water equal to its volume.
  45. Give reason: Objects weigh less in water than in air.
    Answer: Because water exerts an upward buoyant force.
  46. Give reason: Mercury sinks in water.
    Answer: Because its density (13.6 g/cm³) is much higher than water.
  47. Give reason: Volume of irregular solids is not calculated by formula.
    Answer: Because they lack regular shape with measurable dimensions.
  48. Give reason: A balloon stops rising after a point in the atmosphere.
    Answer: Because the air becomes less dense and buoyant force balances the weight.
  49. Give reason: Relative density is used to compare substances.
    Answer: Because it gives a standard ratio to compare densities with water.
  50. Give reason: Oil and water form two layers.
    Answer: Because they are immiscible and have different densities.

Arrange the Words 

Case Studies

  1. A student drops a metal cube of side 2 cm and mass 32 g into a measuring cylinder already containing 40 cm³ of water. The new water level rises to 48 cm³.
    What is the density of the cube?
    Answer: Volume = 8 cm³ (48 – 40), Mass = 32 g, Density = 32 ÷ 8 = 4 g/cm³
  2. A stone weighs 100 g in air and 80 g when immersed in water.
    Calculate the upthrust on the stone.
    Answer: Upthrust = 100 g – 80 g = 20 g
  3. A density bottle weighs 40 g empty, 90 g when filled with water, and 84 g when filled with oil.
    Find the density of oil.
    Answer:
     Mass of oil = 84 – 40 = 44 g
     Mass of water = 90 – 40 = 50 g
     Density of oil = (44/50) × 1 = 0.88 g/cm³
  4. A plastic block of mass 15 g and volume 30 cm³ is thrown into water.
    Will it float or sink?
    Answer: Density = 15/30 = 0.5 g/cm³ < 1 → It will float
  5. A wooden block floats with 75% of its volume submerged.
    What is its relative density?
    Answer: Relative density = 0.75
  6. An object sinks in water but floats in mercury.
    What can you infer about its density?
    Answer: Density > 1 g/cm³ but < 13.6 g/cm³ → It is denser than water but less dense than mercury
  7. A gold coin weighs 80 g and occupies a volume of 4.2 cm³.
    Find the density of gold and state if it is pure (Use standard: 19.3 g/cm³).
    Answer: Density = 80 ÷ 4.2 ≈ 19.05 g/cm³ → It is nearly pure
  8. A student notes a decrease in weight when an object is submerged in water.
    What principle does this demonstrate?
    Answer: Archimedes’ Principle
  9. A measuring cylinder contains 50 cm³ of water. A stone is dropped into it and water rises to 65 cm³.
    Calculate volume of the stone.
    Answer: 65 – 50 = 15 cm³
  10. A submarine adjusts its depth in the sea by varying its average density.
    Which mechanism allows this?
    Answer: Ballast tanks
  11. A boy uses a beaker and a measuring cylinder to measure volume. He finds different readings.
    Which is more accurate and why?
    Answer: Measuring cylinder, because it has finer graduation
  12. A balloon filled with hot air rises in the sky.
    Why does this happen?
    Answer: Hot air is less dense than surrounding cold air
  13. An iceberg floats with a large part submerged.
    Why does this happen despite it being solid?
    Answer: Density of ice is less than water (0.92 g/cm³)
  14. A student calculates density as 0.78 g/cm³. Will the object sink or float in water?
    Answer: Since 0.78 < 1 → It will float
  15. A student gets different densities for the same object using different vessels.
    What could be the reason?
    Answer: Parallax error or incorrect volume measurement
  16. A steel needle sinks in water, but a ship floats.
    Explain the contradiction.
    Answer: Ship’s average density is less than water due to hollow shape
  17. A cork piece has mass 5 g and volume 15 cm³.
    Will it float or sink in water?
    Answer: Density = 5/15 = 0.33 g/cm³ → It will float
  18. A student uses a density bottle and finds mass of water = 50 g, mass of unknown liquid = 40 g.
    Find the relative density of the unknown liquid.
    Answer: 40 ÷ 50 = 0.8
  19. A substance has a relative density of 2.5.
    What does this imply?
    Answer: It is 2.5 times denser than water and will sink
  20. A whale rises to the surface and floats.
    What physical principle helps it float?
    Answer: Buoyant force due to water displacing its volume

Numericals

Numeric problems are not available for this chapter.

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