S3 Science: Pressure, Upthrust And Floating (Paper 2 (intermediate))

S3 Science: Pressure, Upthrust and Floating (Paper 2 (intermediate))

2026-11-14

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Tutor Prep Guide · Pressure as force over area, pressure in liquids changing with depth, atmospheric pressure and the ten metre water column, the principle of upthrust and displaced fluid, density and floating, apparent weight and displacement

S3 Science: Pressure, Upthrust and Floating (Paper 2 (intermediate))

This paper combines formulas with situations: pressure from density times g times depth, total force from pressure times area, upthrust from displaced liquid, submerged fraction from a density ratio, and the difference in upthrust between seawater and fresh water.

Direct answers　Pressure in a liquid is density times g times depth; total force is pressure times area; upthrust is the weight of displaced liquid; the submerged fraction equals the density ratio; gases also give upthrust.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S3 Science: Pressure, Upthrust and Floating
Level	S3

02　Questions (10 items)

FoundationWhat is the water pressure at a depth of 2 m? (water density 1000 kg/m³, g = 10 N/kg)
FoundationA submarine window of area 0.02 square metres is 5 m deep. What total force does the water exert on it?
FoundationA floating body at rest displaces 300 cubic centimetres of water. What is its weight? (g = 10 N/kg)
IntermediateA force of 400 N acts on 0.2 square metres. What is the pressure, and what does it become if the area is reduced to 0.05 square metres?
IntermediateMercury has a density of 13600 kg/m³. What pressure does 0.1 m of mercury produce? (g = 10 N/kg)
IntermediateA log of volume 0.5 cubic metres and density 600 kg/m³ floats on water. What upthrust acts on it? (g = 10 N/kg)
ChallengeIce has a density of 0.92 g/cm³. For an iceberg of total volume 1000 cubic metres, what volumes lie below and above the surface?
ChallengeAn iron block of volume 100 cubic centimetres (density 7.9 g/cm³) is fully immersed in water. Find the upthrust and the spring balance reading. (g = 10 N/kg)
ChallengeThe same submarine displaces 1000 cubic metres of liquid. How much does the upthrust differ between seawater (1030 kg/m³) and fresh water (1000 kg/m³)? (g = 10 N/kg)
Error redoA student says upthrust exists only in liquids. Is this correct?

03　Answers and one-line notes

#	Answer	One-line note
1	20000 Pa	Density times g times depth gives 1000 times 10 times 2, which is 20000 pascals.
2	1000 N	The pressure at 5 m is 50000 Pa, and multiplying by 0.02 square metres gives 1000 N.
3	3 N	For a floating body upthrust equals weight, and 0.3 kg of displaced water gives 3 N.
4	2000 Pa, rising to 8000 Pa with the smaller area	Cutting the area to one quarter makes the pressure four times larger.
5	13600 Pa	13600 times 10 times 0.1 gives 13600 pascals, a dense liquid gives high pressure even at small depth.
6	3000 N	Its mass is 300 kg, and for a floating body upthrust equals its weight of 3000 N.
7	920 cubic metres below and 80 cubic metres above the surface	The submerged fraction equals the density ratio 0.92, leaving only 8 per cent above water.
8	Upthrust 1 N and a reading of 6.9 N	The iron weighs 7.9 N, 100 cubic centimetres of displaced water gives 1 N of upthrust, so the apparent weight is 6.9 N.
9	They differ by 300000 N: 10300000 N in seawater and 10000000 N in fresh water	With the same displaced volume, a denser liquid gives a larger upthrust.
10	No: gases also produce upthrust, which is how hot air balloons and helium balloons rise	Every fluid, liquid or gas, exerts upthrust on an immersed body.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

In pressure questions separate force in newtons from pressure in pascals and check whether the area is divided; in floating questions compare the density of the object with that of the liquid, or find upthrust from the weight of displaced fluid.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.