A cyclist freewheels down a hill and then gradually comes to a stop on a flat road. Describe the energy transfers that take place from the moment the cyclist begins to freewheel down the hill until they come to a complete stop, referring to useful and waste energy transfers.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A cyclist at the top of a hill stops pedalling and freewheels down the slope. At the bottom of the hill the road becomes flat and the cyclist eventually comes to a complete stop.
Model answer (4 marks)
Gravitational potential energy is converted into kinetic energy as the cyclist freewheels down the hill.
On the flat road the kinetic energy is transferred to thermal or heat energy by friction between the wheels and the road, the brakes and the air resistance.
The heat energy produced by friction is a waste energy transfer because it does not help the cyclist move forward.
Throughout the whole process the total energy is conserved – energy is only transferred between different forms.
On the flat road the kinetic energy is transferred to thermal or heat energy by friction between the wheels and the road, the brakes and the air resistance.
The heat energy produced by friction is a waste energy transfer because it does not help the cyclist move forward.
Throughout the whole process the total energy is conserved – energy is only transferred between different forms.
Examiner tips
- Use the word "converted" or "transferred" to show the change of energy stores.
- Mention both kinetic and thermal energy explicitly.
- Show that the heat energy is waste by stating it does not aid motion.
- Remember the conservation of energy – no energy is created or destroyed.
Common mistakes
- Confusing potential energy with kinetic energy at the start.
- Forgetting to identify the heat energy as waste.
- Leaving out the conservation of energy statement.
Mark scheme (4 marks)
- Gravitational potential energy is transferred to kinetic energy as the cyclist moves down the hill
- As the cyclist travels along the flat road, kinetic energy is transferred to thermal/heat energy due to friction (between brakes/wheels and road / air resistance)
- The thermal/heat energy produced by friction is a waste energy transfer because it does not serve the purpose of moving the cyclist forward
- The total energy is conserved throughout — energy is not created or destroyed, only transferred between stores
Key terms in this question
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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