A cyclist rides along a flat road and then freewheels (stops pedalling) up a hill until coming to rest at the top. Explain the energy transfers that take place from the moment the cyclist stops pedalling until they come to rest at the top of the hill.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A cyclist travelling at a constant speed along a flat road stops pedalling and freewheels up a hill, coming to rest at the top. The hill is rough, so friction and air resistance act on the cyclist throughout.
Model answer (5 marks)
1. At the bottom of the hill the cyclist has kinetic energy (½mv²). 2. As the cyclist climbs, this kinetic energy is converted into gravitational potential energy (mgh). 3. Simultaneously, friction between the tyres and the road and air resistance convert part of the kinetic energy into thermal energy, heating the tyres, air and the cyclist’s body. 4. Consequently the kinetic energy decreases to zero because it is shared between the gravitational potential energy and the thermal energy store. 5. The total energy of the system is conserved; energy is merely transferred between kinetic, potential and thermal forms.
Examiner tips
- Use the exact terms kinetic, potential, thermal energy; show the energy flow; mention friction and air resistance explicitly; keep answer concise and point‑wise; include conservation of energy statement.
Common mistakes
- Confusing kinetic energy with work done; forgetting to mention friction/air resistance; not stating that total energy is conserved.
Mark scheme (5 marks)
- The cyclist has kinetic energy at the bottom of the hill (when they stop pedalling)
- Kinetic energy is transferred to gravitational potential energy as the cyclist gains height
- Energy is also transferred to the thermal energy store of the surroundings / cyclist due to friction and air resistance
- The total kinetic energy decreases (to zero) because it is shared between gravitational potential energy and the thermal energy store
- The total energy is conserved — energy is not created or destroyed, only transferred between stores
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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