A cyclist rides along a flat road and then stops pedalling. The cyclist slows down and eventually comes to a stop. Explain why the cyclist slows down after stopping pedalling, and why the cyclist eventually stops completely.

Eduqas GCSE Physics — 2.3 Forces and motion · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

When the cyclist stops pedalling the forward driving force disappears.

The cyclist is still subject to resistive forces – friction between the tyres and the road, air resistance (drag) and other small forces such as rolling resistance.

These resistive forces are unbalanced: they are greater than any remaining forward force, so a net force acts opposite to the direction of motion.

The resultant opposite force causes the cyclist to decelerate until the velocity reaches zero and the cyclist comes to a complete stop.

Examiner tips

  • Use the word ‘drive’ for the forward force and ‘resistive’ for friction/drag; link the unbalanced forces to deceleration.
  • Show the chain: no driving force → resistive forces remain → net force opposite → deceleration → stop.

Common mistakes

  • Confusing friction with air resistance or vice‑versa; or omitting that the driving force disappears.
  • Failing to state that the net force is opposite to the motion or that it causes deceleration.

Mark scheme (4 marks)

  1. When the cyclist stops pedalling, there is no longer a driving force (forward force)
  2. Friction / air resistance / drag still acts on the cyclist
  3. The resistive forces are unbalanced / greater than the driving force, so there is a resultant force opposing the motion
  4. The resultant force causes the cyclist to decelerate until the velocity reaches zero / cyclist stops

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