OxfordAQA IGCSE Physics: Energy — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Energy study guide, Energy revision notes

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Questions

1. State the equation linking work done, force and distance, and state the unit of work done. [2]

2. A crane lifts a 50 kg load through a height of 12 m. (g = 10 N kg⁻¹) Calculate the gravitational potential energy gained by the load. [3]

3. A 0.50 kg ball moves at 8.0 m s⁻¹.

(a) Calculate its kinetic energy. [3] (b) State, without recalculating, what happens to the kinetic energy if the speed is doubled and the mass stays the same. [1]

4. A motor is supplied with 800 J of energy and does 600 J of useful work in 4.0 s.

(a) Calculate the efficiency of the motor as a percentage. [2] (b) Calculate the useful power output of the motor. [2]

5. Describe how a Sankey diagram would represent the energy transfer in Question 4, stating the energy value each branch would represent. [3]

6. An object of mass 2.0 kg is released from rest and falls freely through a height of 5.0 m. (g = 10 N kg⁻¹, assume no air resistance)

(a) Calculate the gravitational potential energy lost by the object. [2] (b) Use your answer to (a) to calculate the object’s speed just before it hits the ground. [3]

7. Explain the difference between power and energy, and explain why a device with a higher power rating does not necessarily transfer more total energy than a lower-powered device. [3]

8. A remote island community is considering solar power and geothermal power as new energy resources. The island receives strong, consistent sunshine year-round but has no accessible geothermal activity nearby. Using this information, explain which resource is the more suitable choice, referring to one advantage and one drawback of each. [4]

9. A ball is dropped and allowed to bounce repeatedly; each bounce is lower than the last, until the ball eventually stops bouncing altogether. Using the term dissipated, explain what has happened to the ball’s original energy. [3]

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Answers

1. Work done = force × distance (W = Fd) [1]. The unit of work done is the joule (J) [1].

2. Ep = mgh = 50 × 10 × 12 [1] [1] = 6000 J [1].

3. (a) Ek = ½mv² = ½ × 0.50 × 8.0² [1] [1] = 16 J [1]. (b) The kinetic energy would become four times as large (64 J), since doubling speed quadruples kinetic energy at constant mass [1].

4. (a) Efficiency = useful energy output ÷ total energy input = 600 ÷ 800 [1] = 75% [1]. (b) Power = energy ÷ time = 600 ÷ 4.0 [1] = 150 W [1].

5. The input arrow would be 800 J wide, representing the total energy supplied [1]. This would split into a wider branch of 600 J, representing the useful work done [1], and a narrower branch of 200 J, representing the energy dissipated (wasted, typically as heat) [1].

6. (a) Ep = mgh = 2.0 × 10 × 5.0 [1] = 100 J [1]. (b) Since air resistance is ignored, all of the gravitational potential energy lost is transferred to kinetic energy: Ek = 100 J [1]. ½mv² = 100, so v² = (2 × 100) ÷ 2.0 = 100 [1], giving v = 10 m s⁻¹ [1].

7. Power is the rate at which energy is transferred or work is done (measured in watts), while energy is the total amount transferred (measured in joules) [1] [1]. A higher-powered device transfers energy faster, but only transfers more total energy than a lower-powered device if both run for the same length of time — run for long enough, a lower-powered device can transfer just as much total energy [1].

8. Solar power is the more suitable choice [1]. Advantage of solar: the island’s strong, consistent sunshine means a solar installation would generate electricity reliably for most of the year [1]. Drawback of geothermal: it requires suitable geology (accessible hot rock close to the surface), which the island does not have, making it impractical or very costly to access [1]. A brief acknowledged drawback of solar (such as generating no electricity at night) does not outweigh the fact that geothermal is not a realistic option here at all [1].

9. The ball’s original gravitational potential energy was transferred to kinetic energy as it fell, and then to elastic potential energy briefly on each bounce [1], but with every bounce, some of this energy is dissipated — spread out into the surroundings, mostly as heat and sound, due to resistive forces such as air resistance and energy lost within the ball and the surface on each impact [1]. The energy is never destroyed, only transferred and dissipated into less useful forms, which is why the ball’s bounces get progressively lower until none of the original energy remains in a useful, recoverable form [1].

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Where marks are usually lost

• Confusing power (rate of energy transfer, in watts) with energy itself (in joules).
• Forgetting that doubling speed quadruples kinetic energy, not doubles it.
• Sankey diagram answers that do not account for all of the input energy across the branches.
• Describing energy as “lost” instead of transferred or dissipated.
• Chaining the gravitational potential energy and kinetic energy equations incorrectly, or forgetting to take a square root when finding speed.
• Giving a generic list of renewable/non-renewable pros and cons instead of a reasoned comparison for the specific scenario given.

Approaching Energy calculation questions

The four core equations in this topic — work, gravitational potential energy, kinetic energy and power — are frequently combined rather than tested in isolation, so the most valuable practice is working through multi-step problems like Question 6, where the output of one equation becomes the input to another. Before calculating, identify which quantities are known and which equation connects them to the quantity being asked for, since misidentifying this is a more common source of lost marks than an arithmetic error once the right equation is chosen. For efficiency and Sankey diagram questions, always check that the useful and wasted branches sum back to the total input energy — this simple check catches most errors before they reach the final answer.