Practise 29 real questions on Forces, density and pressure from 2021 to 2024. See the answer and explanation as soon as you answer.
Forces, density and pressure is one of the 13 main topics in our A Level Physics (Cambridge (CAIE) 9702) question bank, and about 4% of its real questions come from it. Tayyari Karo has 29 real questions on this topic from 2021 to 2024, from Paper 1, Paper 2; 26 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 16 medium, 11 hard, 2 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
A thin horizontal plate of area 0.036 m² is beneath the surface of a liquid of density 930 kg m⁻³. The force on one side of the plate due to the pressure of the liquid is 290 N.
What is the depth of the plate beneath the surface of the liquid?
Answer: A. 0.88 m
pressure p = F/A = 290/0.036 = 8056 Pa; p = ρgh, so h = p/(ρg) = 8056/(930 × 9.81) = 0.88 m.
A uniform bar of weight 200 N and length 4.0 m is freely hinged on a wall at one end. The bar is horizontal and held in equilibrium by a cable attached 0.50 m from the other end. The cable is at 35° to the horizontal.
What is the tension T in the cable?
Answer: C. 200 N
Taking moments about the hinge: T sin35° × 3.5 = 200 × 2.0, so T = 400/(3.5×sin35°) ≈ 200 N.
An object of weight W is suspended from a newton meter. When completely immersed in water, the newton meter reads P. When completely immersed in oil, it reads Q.
What is the ratio (density of oil)/(density of water)?
Answer: D. (W−Q)/(W−P)
Upthrust = weight − reading, and upthrust ∝ fluid density for the same submerged volume, so density(oil)/density(water) = (W−Q)/(W−P).
When must an object be in equilibrium?
Answer: B. when no resultant force and no resultant torque act on the object
Full equilibrium requires both zero resultant force AND zero resultant torque (moment).
A mixture consists of 1200 kg of oil of density 1100 kg m⁻³, 1500 kg of oil of density 860 kg m⁻³, and 4000 kg of oil of density 910 kg m⁻³. No chemical activity occurs. What is the density of the mixture?
Answer: A. 927 kg m⁻³
Total mass = 6700 kg. Total volume = 1200/1100 + 1500/860 + 4000/910 = 1.0909+1.7442+4.3956 = 7.2307 m³. Density = 6700/7.2307 ≈ 927 kg m⁻³.
Which pair of forces forms a couple with a torque of 30 N m? (A: two anti-parallel 30 N forces separated by 2.0 m; B: an unequal pair, 40 N and 10 N, separated by 1.0 m; C: an unequal pair, 25 N and 5 N, separated by 1.0 m; D: two anti-parallel 15 N forces separated by 2.0 m)
Answer: D. 15 N and 15 N forces, 2.0 m apart
A couple requires two equal, anti-parallel forces. Only D has equal forces (15 N each); torque = 15 × 2.0 = 30 N m.
| Session | Paper 1 | Paper 2 |
|---|---|---|
| May/June 2024 | 4 | 1 |
| October/November 2024 | 3 | – |
| October/November 2023 | 4 | 1 |
| May/June 2022 | 7 | 1 |
| October/November 2022 | 5 | – |
| May/June 2021 | 3 | – |
29 real A Level Physics (9702) questions on Forces, density and pressure from 2021 to 2024, from Paper 1, Paper 2. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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