A cyclist rides along a flat road at a constant speed. The cyclist then stops pedalling but continues to slow down until coming to rest. Explain why the cyclist slows down and describe what happens to the kinetic energy of the cyclist as they come to rest.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A cyclist travelling at a steady speed on a flat road stops pedalling. The cyclist gradually decelerates and eventually stops.
Model answer (5 marks)
1. A resistive force (friction between the tyres and the road, and air resistance) acts opposite to the direction of motion.
2. Because the cyclist stops pedalling, no additional force is applied to counter this resistive force.
3. The resistive force does negative work on the cyclist, removing mechanical energy from the system.
4. The kinetic energy of the cyclist decreases; the lost energy is transferred to the surroundings as thermal (heat) energy.
5. When the cyclist comes to rest, all of the initial kinetic energy has been dissipated and the kinetic energy is zero.
2. Because the cyclist stops pedalling, no additional force is applied to counter this resistive force.
3. The resistive force does negative work on the cyclist, removing mechanical energy from the system.
4. The kinetic energy of the cyclist decreases; the lost energy is transferred to the surroundings as thermal (heat) energy.
5. When the cyclist comes to rest, all of the initial kinetic energy has been dissipated and the kinetic energy is zero.
Examiner tips
- Use the word "resistive" and name both tyre‑road friction and air resistance. Show that the work done by the resistive force is negative. Explain that the energy is converted to heat, not lost. End with the kinetic energy being zero at rest.
Common mistakes
- Forgetting to mention both tyre‑road friction and air resistance. Saying the energy is "lost" instead of "converted to heat". Leaving out that the kinetic energy is zero when the cyclist stops.
Mark scheme (5 marks)
- A resistive force (friction / air resistance) acts on the cyclist opposing their motion
- The cyclist does work against the resistive force
- The kinetic energy of the cyclist decreases / is transferred away as the cyclist slows down
- The kinetic energy is dissipated as thermal (heat) energy to the surroundings
- When the cyclist is at rest, all kinetic energy has been transferred / kinetic energy is zero
Key terms in this question
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Particle accelerators and detectors questions
- A delivery drone uses an electric motor to hover in place, holding a parcel at a…
- A petrol-powered go-kart engine transfers 12 000 J of chemical energy every seco…
- A motor is used to lift boxes onto a shelf in a warehouse. For every 400 J of el…
- A student pushes a heavy crate across a rough floor. The crate moves at a consta…