IGCSE Physics 1.4 Density MCQs – 30 Practice Questions with Answers (Cambridge 0625)

These 30 original practice questions cover Cambridge IGCSE Physics (0625) Section 1.4, Density: calculating density with ρ = m/V in kg/m3 and g/cm3, measuring the density of solids and liquids, and using density to explain floating and sinking. Every question has a worked answer – tap “Show Answer” to check yourself.

Formula recap: density ρ = mass / volume. Need the full equation list? See the IGCSE Physics Formula Sheet.

Density Calculations

Q1. Density is defined by the equation

  • (A) density = mass / volume
  • (B) density = volume / mass
  • (C) density = mass × volume
  • (D) density = mass × area
Show Answer

Answer: A – Density ρ = m/V. In SI units, mass in kg divided by volume in m3 gives density in kg/m3.

Q2. A metal block has mass 540 g and volume 200 cm3. Its density is

  • (A) 0.37 g/cm3
  • (B) 2.7 g/cm3
  • (C) 27 g/cm3
  • (D) 108 000 g/cm3
Show Answer

Answer: B – ρ = m/V = 540 / 200 = 2.7 g/cm3. This is the density of aluminium.

Q3. A density of 2.7 g/cm3 expressed in kg/m3 is

  • (A) 2.7 kg/m3
  • (B) 27 kg/m3
  • (C) 270 kg/m3
  • (D) 2700 kg/m3
Show Answer

Answer: D – 1 g/cm3 = 1000 kg/m3, so 2.7 g/cm3 = 2.7 × 1000 = 2700 kg/m3. To convert g/cm3 to kg/m3, multiply by 1000.

Q4. A solid aluminium part has volume 0.50 m3. The density of aluminium is 2700 kg/m3. Its mass is

  • (A) 1350 kg
  • (B) 5400 kg
  • (C) 135 kg
  • (D) 0.000185 kg
Show Answer

Answer: A – Rearrange ρ = m/V to m = ρV = 2700 × 0.50 = 1350 kg.

Q5. The density of gold is 19.3 g/cm3. The volume of a gold bar of mass 193 g is

  • (A) 1.0 cm3
  • (B) 10 cm3
  • (C) 100 cm3
  • (D) 3725 cm3
Show Answer

Answer: B – V = m/ρ = 193 / 19.3 = 10 cm3. Gold is very dense (19 300 kg/m3), so even a heavy bar has a small volume.

Q6. A volume of 250 cm3 expressed in m3 is

  • (A) 0.25 m3
  • (B) 2.5 × 10−2 m3
  • (C) 2.5 × 10−4 m3
  • (D) 2.5 × 102 m3
Show Answer

Answer: C – 1 cm = 10−2 m, so 1 cm3 = (10−2)3 = 10−6 m3. Then 250 cm3 = 250 × 10−6 = 2.5 × 10−4 m3. The classic trap is dividing by 100 instead of 106.

Q7. A liquid of mass 240 g occupies a volume of 300 cm3. Its density is

  • (A) 0.80 g/cm3
  • (B) 1.25 g/cm3
  • (C) 8.0 g/cm3
  • (D) 0.080 g/cm3
Show Answer

Answer: A – ρ = m/V = 240 / 300 = 0.80 g/cm3, which is 800 kg/m3 – less than water, so this liquid would float on water.

Q8. Material X has density 0.92 g/cm3. Material Y has density 850 kg/m3. Which statement is correct?

  • (A) Y is denser than X
  • (B) X and Y have equal densities
  • (C) X is denser than Y
  • (D) The densities cannot be compared in different units
Show Answer

Answer: C – Convert X: 0.92 g/cm3 = 0.92 × 1000 = 920 kg/m3, which is greater than 850 kg/m3, so X is denser. Always convert to the same unit before comparing.

Q9. A piece of metal has mass 780 g and density 7.8 g/cm3. Its volume is

  • (A) 10 cm3
  • (B) 100 cm3
  • (C) 1000 cm3
  • (D) 6084 cm3
Show Answer

Answer: B – V = m/ρ = 780 / 7.8 = 100 cm3. (This density is that of iron/steel.)

Q10. A block measuring 0.10 m × 0.050 m × 0.020 m has mass 2.0 kg. Its density in kg/m3 is

  • (A) 20 kg/m3
  • (B) 200 kg/m3
  • (C) 2000 kg/m3
  • (D) 20 000 kg/m3
Show Answer

Answer: D – V = 0.10 × 0.050 × 0.020 = 1.0 × 10−4 m3. ρ = m/V = 2.0 / (1.0 × 10−4) = 20 000 kg/m3 – a very dense metal, close to gold.

Measuring Density

Q11. To find the density of a regular metal cube, a student should

  • (A) measure its mass on a balance and one side with a ruler, then cube the side to get the volume
  • (B) measure its mass on a balance and guess the volume
  • (C) put it in water and weigh the water it pushes out
  • (D) measure the side with a ruler only – the mass is not needed
Show Answer

Answer: A – For a regular solid, volume = length × width × height (for a cube, side3), measured with a ruler; mass comes from a balance. Then ρ = m/V.

Q12. A student measures the volume of an irregular stone by displacement in a measuring cylinder. The correct method is to

  • (A) read the water level, lower the stone in until it is fully under the water, read the new level, and subtract
  • (B) read the water level, add the stone, and take the first reading as the volume
  • (C) fill the cylinder to the top, add the stone, and read the level
  • (D) weigh the cylinder before and after adding the stone
Show Answer

Answer: A – The rise in level = final level − initial level = volume of the stone, provided the stone is fully submerged and does not dissolve or absorb water.

Q13. When reading the volume in a measuring cylinder, the reading is most accurate when

  • (A) you look down at the surface from above
  • (B) you look up at the surface from below
  • (C) your eye is level with the bottom of the meniscus
  • (D) the cylinder is held in your hand and tilted
Show Answer

Answer: C – Reading with the eye level with the bottom of the meniscus avoids parallax error. The cylinder should stand on a flat bench.

Q14. An empty measuring cylinder has mass 50 g. With 100 cm3 of a liquid in it, the mass is 130 g. The density of the liquid is

  • (A) 1.3 g/cm3
  • (B) 0.50 g/cm3
  • (C) 8.0 g/cm3
  • (D) 0.80 g/cm3
Show Answer

Answer: D – Mass of liquid = 130 − 50 = 80 g. ρ = 80 / 100 = 0.80 g/cm3. The trap is forgetting to subtract the mass of the empty cylinder (which would give the wrong answer 1.3).

Q15. The displacement method works because

  • (A) the mass of water displaced equals the mass of the object
  • (B) the volume of water displaced equals the volume of the submerged object
  • (C) the density of water is exactly 1 g/cm3
  • (D) the object always sinks in water
Show Answer

Answer: B – A submerged object pushes aside (“displaces”) a volume of water exactly equal to its own volume, so the rise in level in the cylinder gives the object’s volume directly.

Q16. A stone has a volume of about 15 cm3. Which measuring cylinder gives the most accurate measurement of its volume by displacement?

  • (A) A 1000 cm3 cylinder with 50 cm3 graduations
  • (B) A 500 cm3 cylinder with 10 cm3 graduations
  • (C) A 250 cm3 cylinder with 5 cm3 graduations
  • (D) A 50 cm3 cylinder with 1 cm3 graduations
Show Answer

Answer: D – In a narrow cylinder the same volume causes a bigger rise in level, and the smallest graduations give the finest readings, so the percentage uncertainty is smallest. The cylinder must still be big enough to hold the stone and the water.

Q17. A student pours a powder into a measuring cylinder and reads its “volume” from the top surface of the powder. The calculated density will be too low because

  • (A) the powder has no mass
  • (B) powders are always less dense than solids
  • (C) the balance reads the mass too high
  • (D) the measured volume includes air gaps between the grains, so the volume is too large
Show Answer

Answer: D – The reading includes trapped air between the grains, so V is overestimated. Since ρ = m/V, an overestimated volume gives an underestimated density.

Q18. Which method gives a basic measurement of the density of a gas?

  • (A) Trap the gas over water and read its colour
  • (B) Weigh a sealed flask of known volume full of the gas, then weigh it again with the gas pumped out; the difference in mass is the mass of the gas
  • (C) Measure the gas with a ruler and weigh it on an open balance
  • (D) A gas has no mass, so its density cannot be measured
Show Answer

Answer: B – Gases do have mass, but it is small, so a sensitive balance is used: mass of gas = (mass of flask + gas) − (mass of empty flask), and the volume is the known volume of the flask.

Q19. In a displacement experiment, an air bubble is clinging to the stone when it is lowered into the water. The calculated density of the stone will be

  • (A) too large, because the measured volume is too small
  • (B) too large, because the measured mass is too big
  • (C) too small, because the measured volume is too large
  • (D) unaffected, because air has no volume
Show Answer

Answer: C – The bubble adds to the displaced volume, so the rise in level is bigger than the stone’s true volume. With V too large, ρ = m/V comes out too small. Shake or brush bubbles off before reading.

Q20. A stone of mass 39 g is lowered into a measuring cylinder. The water level rises from 40 cm3 to 55 cm3. The density of the stone is

  • (A) 2.6 g/cm3
  • (B) 0.71 g/cm3
  • (C) 0.98 g/cm3
  • (D) 1.4 g/cm3
Show Answer

Answer: A – V = 55 − 40 = 15 cm3. ρ = m/V = 39 / 15 = 2.6 g/cm3.


Floating, Sinking & Applications

Q21. An object will float in a liquid if

  • (A) its mass is less than the mass of the liquid
  • (B) its volume is less than the volume of the liquid
  • (C) its density is less than the density of the liquid
  • (D) it is smaller than the container
Show Answer

Answer: C – Floating and sinking depend on density only: density of object less than density of liquid means it floats; greater means it sinks.

Q22. [Supplement] Ice has density 920 kg/m3 and water has density 1000 kg/m3. When ice floats in water, the fraction of the ice below the surface is about

  • (A) 8%
  • (B) 50%
  • (C) 92%
  • (D) 100%
Show Answer

Answer: C – A floating object displaces its own weight of liquid, so the submerged fraction = ρice/ρwater = 920/1000 = 0.92, i.e. about 92% is underwater – why icebergs are so dangerous to ships.

Q23. A block of wood has density 600 kg/m3. It is placed in a liquid of density 500 kg/m3. The block will

  • (A) sink
  • (B) float with most of it below the surface
  • (C) float with most of it above the surface
  • (D) stay wherever it is placed
Show Answer

Answer: A – 600 kg/m3 is greater than 500 kg/m3, so the block is denser than the liquid and sinks – even though the same block would float in water (1000 kg/m3).

Q24. A steel ship floats even though steel has density about 7800 kg/m3, much greater than water. This is because

  • (A) steel becomes less dense in water
  • (B) the ship’s average density, including the air inside the hull, is less than the density of water
  • (C) the ship is pushed up by the wind
  • (D) salt water is denser than steel
Show Answer

Answer: B – The hull encloses a large volume of air, so (total mass)/(total volume) for the whole ship is less than 1000 kg/m3. If the hull fills with water, the average density rises above that of water and the ship sinks.

Q25. A hot-air balloon rises when the air inside it is heated because heating

  • (A) increases the density of the air inside
  • (B) removes the air from inside the balloon
  • (C) increases the mass of the air inside
  • (D) decreases the density of the air inside, so the balloon’s overall density becomes less than that of the surrounding air
Show Answer

Answer: D – Heated air expands and some leaves through the opening, so the mass per unit volume (density) inside falls below the density of the cooler air outside, and the balloon rises.

Q26. A submarine dives by filling its ballast tanks with seawater. This works because the water in the tanks

  • (A) decreases the volume of the submarine
  • (B) increases the submarine’s mass without changing its volume, raising its average density above that of seawater
  • (C) pushes the submarine downwards by pressure
  • (D) makes the submarine more streamlined
Show Answer

Answer: B – The volume stays the same but the mass increases, so average density = m/V increases. Once it exceeds the density of seawater, the submarine sinks. To surface, the water is blown out and replaced with air.

Q27. [Supplement] Equal volumes of metal A (density 2000 kg/m3) and metal B (density 6000 kg/m3) are melted together to form an alloy. Assuming the total volume is unchanged, the density of the alloy is

  • (A) 3000 kg/m3
  • (B) 8000 kg/m3
  • (C) 4000 kg/m3
  • (D) 12 000 kg/m3
Show Answer

Answer: C – Take 1 m3 of each: masses are 2000 kg and 6000 kg, total 8000 kg in 2 m3. ρ = 8000/2 = 4000 kg/m3 – the average of the two densities when the volumes are equal.

Q28. A solid has density 1200 kg/m3. Which row is correct?

  • (A) Floats in water (1000 kg/m3), floats in liquid X (1500 kg/m3)
  • (B) Sinks in water (1000 kg/m3), sinks in liquid X (1500 kg/m3)
  • (C) Floats in water (1000 kg/m3), sinks in liquid X (1500 kg/m3)
  • (D) Sinks in water (1000 kg/m3), floats in liquid X (1500 kg/m3)
Show Answer

Answer: D – 1200 is greater than 1000, so it sinks in water; 1200 is less than 1500, so it floats in liquid X.

Q29. A hydrometer is a sealed tube with a scale that floats upright in a liquid to measure its density. The hydrometer floats higher in the liquid when

  • (A) the liquid is denser
  • (B) the liquid is less dense
  • (C) the liquid is warmer, whatever its density
  • (D) the tube is made of heavier glass
Show Answer

Answer: A – In a denser liquid, the hydrometer needs to displace less volume to support its own weight, so it floats higher. Hydrometers are used to check, for example, battery acid and milk.

Q30. A ship sails from the sea (salt water, density about 1025 kg/m3) into a river (fresh water, density 1000 kg/m3) with the same load. In the river the ship will

  • (A) float higher, with less of the hull underwater
  • (B) float at exactly the same level
  • (C) sink lower, with more of the hull underwater
  • (D) sink completely
Show Answer

Answer: C – Fresh water is less dense, so the ship must displace a larger volume of it to support the same weight – it sits lower in the water. This is why load (Plimsoll) lines mark different safe levels for salt and fresh water.

Keep practising: revise every equation on the IGCSE Physics Formula Sheet, and find topic pages for all boards on the Physics MCQs hub.

All questions on this page are original practice questions written for QuaidianPoint. They are not Cambridge past-paper questions.