A wind-up toy car is released and moves across a flat floor until it stops. Describe the energy transfers that occur from the moment the spring is fully wound to the moment the car comes to rest, naming the energy stores involved at each stage.

Pearson Edexcel International GCSE Physics (4PH1) — 4.1 Energy transfers · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A child winds up a small toy car by turning a key, which compresses a spring inside the car. When released, the car moves across a flat floor and gradually slows to a stop.

Model answer (4 marks)

1. The wound spring stores elastic potential energy.
2. As the spring unwinds, that elastic potential energy is converted into kinetic energy of the car.
3. While the car moves, friction between the wheels, axle and floor converts kinetic energy into thermal energy.
4. The total energy is conserved; the energy is simply transferred between stores, with the final energy appearing as heat in the surroundings.

Examiner tips

  • Use the exact terms: elastic potential energy, kinetic energy, thermal energy. Show the sequence of transfers. Mention conservation of energy at the end.

Common mistakes

  • Confusing potential energy with kinetic energy. Forgetting to mention the thermal energy store. Claiming energy is destroyed instead of transferred.

Mark scheme (4 marks)

  1. The wound spring stores elastic potential energy
  2. Elastic potential energy is transferred to kinetic energy (as the spring unwinds and the car moves)
  3. As the car slows, kinetic energy is transferred to thermal energy (due to friction between the wheels/axle and surfaces)
  4. The total energy is conserved throughout / no energy is created or destroyed (energy is dissipated to the surroundings as thermal energy)

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