AS Level Physics chapter 4: Forces, density and pressure MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
69 exam-style questions on Forces, density and pressure, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Forces, density and pressure questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A force acts on a lever at an angle to it. Which change on its own doubles the moment of the force about the pivot?
A
doubling the force and halving its distance from the pivot
B
doubling the angle between the force and the lever from 30° to 60°
C
moving the force so that its line of action passes through the pivot
D
doubling the perpendicular distance from the pivot to the line of action
Show answer
Answer: D. Moment = F × perpendicular distance, so doubling that distance doubles the moment. Doubling 30° to 60° multiplies sin θ by only 1.73, and a line of action through the pivot gives zero moment.
2. A cube of side 0.10 m is held fully submerged in water (density 1000 kg m−3) with its top face horizontal and 0.20 m below the surface. Ignoring atmospheric pressure, what is the difference between the forces of the water on its bottom and top faces?
A
9.8 N
B
20 N
C
29 N
D
49 N
Show answer
Answer: A. Pressure on top = ρg(0.20) and on bottom = ρg(0.30), so the force difference = 1000 × 9.81 × 0.10 × 0.010 = 9.8 N, the upthrust. 29 N is the force on the bottom face alone.
3. Equal masses of two liquids, of densities 800 kg m−3 and 1200 kg m−3, are mixed. The total volume does not change on mixing. What is the density of the mixture?
A
960 kg m−3
B
1000 kg m−3
C
1200 kg m−3
D
2000 kg m−3
Show answer
Answer: A. For mass m of each: total volume = m/800 + m/1200, so density = 2m ÷ (m/800 + m/1200) = 960 kg m−3. The simple average, 1000 kg m−3, is correct only for equal volumes.
4. A door is opened by a force of 25 N applied at right angles to the door, 0.80 m from the hinge. What force, applied at right angles 0.50 m from the hinge, gives the same moment?
A
16 N
B
25 N
C
40 N
D
50 N
Show answer
Answer: C. Moment = 25 × 0.80 = 20 N m. At 0.50 m: F = 20 ÷ 0.50 = 40 N. A smaller distance needs a larger force.
5. In which case is the turning effect produced by a single force rather than by a couple?
A
two fingers turning a tap handle from opposite sides
B
one hand pushing a door at its handle while the hinges hold the door
C
a magnetic compass needle turned by the Earth's field acting on its two poles
D
two hands turning a steering wheel from opposite sides
Show answer
Answer: B. Pushing a door applies one force; the hinge supplies a reaction, and the resultant force is not zero. The other three each involve two equal, opposite, parallel forces with separate lines of action.
6. Two forces of equal size act in opposite directions on an object, but their lines of action are 0.20 m apart. Which statement is correct?
A
the object is in equilibrium because the resultant force is zero
B
the object is not in equilibrium because the resultant force is not zero
C
the object is in equilibrium only if it is at rest
D
the object is not in equilibrium because there is a resultant torque
Show answer
Answer: D. Equilibrium needs zero resultant force and zero resultant torque. These forces form a couple, so the torque is not zero and the object starts to rotate.
7. A student finds the density of a pebble from its mass, (50.0 ± 0.5) g, and its volume, (20 ± 1) cm3. What is the percentage uncertainty in the density?
A
1%
B
4%
C
5%
D
6%
Show answer
Answer: D. For a quotient the percentage uncertainties add: 0.5/50.0 = 1% and 1/20 = 5%, giving 6%. Subtracting them gives 4%.
8. A cube of side 0.10 m has a mass of 2.7 kg. What is its density?
9. Three coplanar forces of 3.0 N, 4.0 N and 5.0 N act on an object that is in equilibrium. What is the angle between the lines of action of the 3.0 N and 4.0 N forces?
A
37°
B
53°
C
90°
D
180°
Show answer
Answer: C. In equilibrium the three forces form a closed triangle, and 3, 4, 5 is a right-angled triangle. The 3.0 N and 4.0 N forces are therefore at 90° to each other.
10. What are the SI base units of pressure?
A
kg m s−2
B
kg m−1 s−2
C
kg m−2 s−2
D
kg m2 s−2
Show answer
Answer: B. Pressure = force ÷ area = (kg m s−2) ÷ m2 = kg m−1 s−2. kg m s−2 is the newton and kg m2 s−2 is the joule.
Forces, density and pressure: questions students ask
How many Forces, density and pressure MCQs are there?
69, each with the answer and a short explanation, across 3 topics: Turning effects of forces, Equilibrium of forces, Density and pressure. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Physics chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
