S3 Science: Pressure, Upthrust And Floating (Paper 3 (challenge))

S3 Science: Pressure, Upthrust and Floating (Paper 3 (challenge))

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 3 (challenge))

This paper handles harder applications: force multiplication in a hydraulic press, atmospheric pressure as a water column, pressure deep in a dam, the very large upthrust on a ship and a submersible, pressure on different faces of a cuboid, and floating decided by comparing densities.

Direct answers　A confined liquid transmits pressure; a 10 m water column is about one atmosphere; pressure is density times g times depth; upthrust is the weight of displaced liquid; a smaller contact area gives a larger pressure; density decides floating.

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)

FoundationA hydraulic press has a small piston of area 0.01 square metres loaded with 10 N and a large piston of area 0.5 square metres. What load can the large piston lift?
FoundationAbout how deep must a water column be to equal one atmosphere? (water density 1000 kg/m³, g = 10 N/kg)
FoundationHow many N/m² is one pascal?
IntermediateWhat water pressure acts on a dam at 20 m depth and how many atmospheres is that? (density 1000 kg/m³, g = 10 N/kg, one atmosphere 100000 Pa)
IntermediateA ship displaces 5000 cubic metres of seawater of density 1030 kg/m³. What upthrust acts on it? (g = 10 N/kg)
IntermediateA cuboid with a base of 0.2 m by 0.1 m weighs 80 N. What is the pressure when it lies flat, and when it stands so that the contact area is 0.1 m by 0.1 m?
ChallengeAn iceberg has a total volume of 1000 cubic metres. What volume shows above water, and why must rescue crews take care?
ChallengeA deep sea submersible displaces 2 cubic metres of seawater of density 1030 kg/m³. What upthrust acts on it? (g = 10 N/kg)
ChallengeAn object of density 1.2 g/cm³ is placed in a liquid of density 1.1 g/cm³, and then in one of density 1.3 g/cm³. What happens in each case?
Error redoA student says a heavier object always receives a larger upthrust. Is this correct?

03　Answers and one-line notes

#	Answer	One-line note
1	500 N	The small piston creates 1000 Pa, and the same pressure acting on 0.5 square metres gives 500 N.
2	About 10 m	A 10 m column of water gives 100000 Pa, close to the atmospheric pressure of 101325 pascals.
3	One pascal equals 1 N/m²	The pascal is defined as one newton per square metre.
4	200000 Pa, about two atmospheres	1000 times 10 times 20 gives 200000 pascals, and dividing by 100000 gives two atmospheres.
5	51500000 N	Upthrust equals the weight of displaced seawater, 5000 times 1030 times 10.
6	4000 Pa lying flat and 8000 Pa standing up	The contact areas are 0.02 and 0.01 square metres, so 80 divided by each gives 4000 and 8000 pascals.
7	80 cubic metres above water, so the visible part is only a small fraction of the hidden mass below	Ice of density 0.92 g/cm³ has 92 per cent of its volume submerged, leaving only 8 per cent visible.
8	20600 N	2 times 1030 times 10 gives 20600 N, and upthrust does not depend on depth, only on displaced liquid.
9	It sinks in the 1.1 g/cm³ liquid and floats in the 1.3 g/cm³ liquid	An object sinks when denser than the liquid and floats when less dense.
10	No: upthrust depends only on the volume of fluid displaced and its density, not on the weight of the object	A heavy stone and a light wooden block displacing the same volume of water receive the same upthrust.

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.