OxfordAQA International GCSE Physics: Work, kinetic, gravitational and elastic energy, and power (9203) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.2.1, Forces and energy (statements a to f), of the OxfordAQA International GCSE Physics (9203) specification, for exams from May/June 2018. The qualification is untiered. Take g = 10 N/kg unless a question gives another value. Work through the study guide first if a topic is new, and use the revision notes for recall. See also the OxfordAQA International GCSE Physics hub, the printable checklist, the Energy practice questions and the free diagnostics.

Questions

1. A dock worker pushes a crate along a level floor.

(a) The worker pushes with a force of 140 N for 7.5 m in the direction of the push. Calculate the work done. [2] (b) A second push does 1800 J of work using a force of 240 N. Calculate the distance moved. [2]

2. A car of mass 1500 kg is travelling at 16 m/s. The driver brakes and the car stops.

(a) Find the kinetic energy of the car at the start of braking. [2] (b) Explain what happens to this energy as the car slows down. [2] (c) The braking force is a constant 8000 N. Calculate the braking distance. [2]

3. A spring has a spring constant of 250 N/m. It is stretched by 0.12 m.

(a) Calculate the elastic potential energy stored in the spring. [2] (b) The extension is doubled to 0.24 m. Calculate the energy stored now, and state how it compares with your answer to part (a). [2] (c) State the condition that must be true for the equation you used to apply. [1]

4. Another spring has a spring constant of 96 N/m and stores 0.75 J of elastic potential energy. Calculate its extension. [3]

5. A crane lifts a load of mass 800 kg through a vertical height of 18 m.

(a) How much gravitational potential energy does the load gain? [2] (b) On the Moon, g is 1.6 N/kg. Find the energy gained by the same load over the same height. [2]

6. A diver of mass 55 kg climbs a ladder and gains 2200 J of gravitational potential energy. Calculate the height climbed. [3]

7. A ball of mass 0.16 kg is kicked and moves at 25 m/s.

(a) Calculate its kinetic energy. [2] (b) A second ball of mass 0.25 kg has 18 J of kinetic energy. Calculate its speed. [3]

8. A car of mass 1000 kg travels at 20 m/s.

(a) Calculate its kinetic energy at 20 m/s and at 40 m/s, and state the factor by which it increases. [3] (b) State the factor by which the kinetic energy changes if the mass is doubled at the same speed. [1] (c) Use your answer to part (a) to explain why driving faster makes a car harder to stop. [1]

9. The motor of an escalator transfers 54 000 J of energy in 30 s.

(a) Calculate the power of the motor. [2] (b) Calculate the time the motor takes to transfer 189 000 J at the same power. [2]

10. A roller coaster car with riders has a total mass of 400 kg. A chain lift raises it through a vertical height of 25 m in 20 s.

(a) Calculate the gravitational potential energy gained by the car. [2] (b) Calculate the power needed to raise it, assuming the work done equals the energy gained. [2] (c) The car then runs down to the bottom. Assume no energy is dissipated. Calculate its speed at the bottom. [3] (d) The measured speed is lower than your answer to part (c). Explain why. [2]

11. A space capsule of mass 1600 kg re-enters the atmosphere at 7200 m/s. Later, its speed has fallen to 250 m/s. Ignore any change in gravitational potential energy.

(a) Calculate the kinetic energy at 7200 m/s. Give your answer to 2 significant figures. [2] (b) Calculate the kinetic energy at 250 m/s. [2] (c) Calculate the energy transferred away from the capsule’s kinetic store. Give your answer to 2 significant figures. [1] (d) Explain what happens to this energy, and why the capsule needs a heat shield. [2]

Answers

1. (a) W = F × d [1] = 140 × 7.5 = 1050 J [1] [2] (b) d = W / F [1] = 1800 / 240 = 7.5 m [1] [2] Examiner insight: answers that start from the equation W = F × d usually show the method clearly, and a unit on the final line is expected for the answer to be complete.

2. (a) Ek = ½ × m × v² = ½ × 1500 × 16² [1] = 192 000 J [1] [2] (b) Friction between the brake pads and discs does work [1]; the kinetic energy is transferred by heating, so the brakes become hot and the energy spreads to the surroundings [1] [2] (c) Work done by brakes = kinetic energy lost, so F × d = 192 000, giving d = 192 000 / 8000 [1] = 24 m [1] [2] Examiner insight: a good part (b) names the force doing the work, friction, and the form the energy takes. “The energy is used up” or “lost” does not say where it went.

3. (a) Ee = ½ × k × e² = ½ × 250 × 0.12² [1] = 1.8 J [1] [2] (b) Ee = ½ × 250 × 0.24² = 7.2 J [1]; this is four times as much [1] [2] (c) The limit of proportionality has not been exceeded (the spring obeys Hooke’s law) [1] [1] Examiner insight: the extension is squared, so doubling it gives four times the energy. Saying “double” is a common slip, and stating the factor shows you understand the equation.

4. e² = 2 × Ee / k [1] = 2 × 0.75 / 96 = 0.015625 [1]; e = 0.125 m [1] [3] Examiner insight: rearranging before substituting lowers the chance of an error. Taking the square root at the end is a step that is often forgotten.

5. (a) Ep = m × g × h = 800 × 10 × 18 [1] = 144 000 J [1] [2] (b) Ep = 800 × 1.6 × 18 [1] = 23 040 J [1] [2] Examiner insight: use the g given in the question for each part. Part (b) shows the mass is the same on the Moon and only the weight changes.

6. h = Ep / (m × g) [1] = 2200 / (55 × 10) [1] = 2200 / 550 = 4.0 m [1] [3] Examiner insight: to find a height from energy, divide by the weight (m × g). Answers that multiply instead of dividing give an unrealistic height.

7. (a) Ek = ½ × 0.16 × 25² [1] = 50 J [1] [2] (b) v² = 2 × Ek / m [1] = 2 × 18 / 0.25 = 144 [1]; v = 12 m/s [1] [3] Examiner insight: in part (b), the speed is found from v squared, so the square root is the last step. Giving v² = 144 as the answer would miss the question.

8. (a) At 20 m/s: ½ × 1000 × 20² = 200 000 J [1]; at 40 m/s: ½ × 1000 × 40² = 800 000 J [1]; factor 4 [1] [3] (b) The kinetic energy is doubled [1] [1] (c) With the same braking force, four times the energy to remove needs four times the braking distance [1] [1] Examiner insight: a road-safety answer that connects the higher kinetic energy to a longer braking distance, with the factor, is stronger than one that says “it is more dangerous”.

9. (a) P = E / t [1] = 54 000 / 30 = 1800 W [1] [2] (b) t = E / P = 189 000 / 1800 [1] = 105 s [1] [2] Examiner insight: the watt is joules per second, so a power answer needs the unit W. Check your time comes out in seconds.

10. (a) Ep = m × g × h = 400 × 10 × 25 [1] = 100 000 J [1] [2] (b) P = W / t = 100 000 / 20 [1] = 5000 W [1] [2] (c) Ek at the bottom = Ep lost, so ½ × 400 × v² = 100 000 [1]; v² = 500 [1]; v = 22.4, so 22 m/s [1] [3] (d) Friction and air resistance act against the motion, doing work [1]; some energy is transferred by heating to the surroundings, so less becomes kinetic energy [1] [2] Examiner insight: in part (c), say clearly that the gravitational potential energy transferred equals the kinetic energy gained. Part (d) gains credit by naming the forces and saying where the energy went.

11. (a) Ek = ½ × 1600 × 7200² [1] = 4.1472 × 10¹⁰, so 4.1 × 10¹⁰ J [1] [2] (b) Ek = ½ × 1600 × 250² [1] = 5.0 × 10⁷ J [1] [2] (c) 4.1472 × 10¹⁰ − 5.0 × 10⁷ = 4.1422 × 10¹⁰, so 4.1 × 10¹⁰ J [1] [1] (d) Air resistance does work against the capsule, so the energy is transferred by heating to the capsule’s surface and the air [1]; the heat shield stops the capsule getting hot enough to be damaged or burn up [1] [2] Examiner insight: standard form with the right power of ten is easy to get wrong. Keep unrounded values in your working and round only the final answer to the number of significant figures asked for.

Where marks are usually lost

• Substituting the whole spring length where the extension belongs.
• Forgetting to square the extension or the speed.
• Saying that doubling speed doubles kinetic energy, when it makes it four times as much.
• Not converting units, such as km/h to m/s, minutes to seconds or cm to m.
• Taking height along a ramp rather than the vertical rise for gravitational potential energy.
• Saying friction “uses up” or “wastes” energy, with no mention of heating or the surroundings.
• Leaving the unit off the answer, or writing J where W is needed.
• Rounding intermediate values, so the final figure is slightly out.
• Writing a bare answer with no equation or working.

Next steps

• Read the revision notes and the study guide.
• Go to the course hub and tick off this topic on the checklist.
• Take the free 10-minute diagnostics to see what to revise next.
• Book a free trial class.

Official syllabus

These questions are aligned to section 3.2.1 of the OxfordAQA International GCSE Physics (9203) specification, for exams May/June 2018 onwards, published by OxfordAQA.