A cyclist rides along a flat road at constant speed, then freewheels (pedals stop turning) up a gentle hill until coming to rest at the top. Describe the energy transfers that occur during each of these two stages of the journey.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
During the flat section the cyclist’s kinetic energy is continuously lost to friction and air resistance, so the rider must do work (input energy) to keep the speed constant.
During the hill section the cyclist’s kinetic energy is converted into gravitational potential energy as the rider climbs, while some of the kinetic energy is still lost as heat to friction and air resistance, which ultimately brings the rider to rest.
During the hill section the cyclist’s kinetic energy is converted into gravitational potential energy as the rider climbs, while some of the kinetic energy is still lost as heat to friction and air resistance, which ultimately brings the rider to rest.
Examiner tips
- Use the word ‘converted’ or ‘transferred’ for energy changes.
- Mention both kinetic to potential and kinetic to thermal for the hill stage.
- Show that work is required on the flat to counter losses.
- Keep the answer brief – one sentence per stage.
Common mistakes
- Confusing kinetic energy with work done by the cyclist.
- Omitting the thermal loss on the hill stage.
- Using ‘energy is lost’ without specifying the type of energy.
Mark scheme (4 marks)
- During the flat section, kinetic energy is transferred to thermal (heat) energy due to friction / air resistance
- During the flat section, the cyclist must do work (input energy) to maintain constant speed because energy is continuously lost to friction / air resistance
- During the hill section, kinetic energy is transferred to gravitational potential energy as the cyclist rises
- During the hill section, kinetic energy is also transferred to thermal (heat) energy due to friction / air resistance, so the cyclist comes to rest
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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