A cyclist is riding along a flat road at a constant velocity. The cyclist then stops pedalling. Explain why the cyclist slows down and eventually stops.

AQA GCSE Physics (8463) — 4.5.6 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 driving force from the chain and pedals disappears.
The friction between the tyres and the road and the air resistance continue to act on the cyclist.
With no forward force, these resistive forces give a net force backwards, opposite to the direction of motion.
According to Newton’s second law this net force causes a deceleration, so the cyclist slows down and eventually stops.

Examiner tips

  • Use the term ‘driving force’ for the pedalling force. Mention both friction and air resistance as resistive forces. Show that the net force is backwards. Link the net force to deceleration via Newton’s second law.

Common mistakes

  • Forgetting to state that the driving force is removed. Confusing the direction of the net force. Not mentioning both friction and air resistance.

Mark scheme (4 marks)

  1. When the cyclist stops pedalling, the driving force is removed / becomes zero
  2. There is still a friction / air resistance force acting on the cyclist
  3. There is now a resultant force acting backwards / in the opposite direction to motion
  4. This resultant force causes a deceleration / causes the cyclist to slow down (Newton's Second Law)

Key terms in this question

velocity

Related

More Forces and motion questions

▶ Try answering this question with AI marking (free) →