A theme park ride lifts passengers in a carriage to the top of a tall tower, then releases the carriage so it falls freely downward. As the carriage falls, it speeds up. Near the bottom, brakes apply a large resistive force to stop the carriage. Explain the energy transfers that occur from the moment the carriage is released at the top until it comes to rest at the bottom.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A theme park ride lifts passengers in a carriage to the top of a tall tower, then releases the carriage so it falls freely downward. As the carriage falls, it speeds up. Near the bottom, brakes apply a large resistive force to stop the carriage.
Model answer (5 marks)
At the top the carriage has gravitational potential energy, GPE = mgh. When released, this GPE is converted into kinetic energy, KE = ½mv², as the carriage accelerates downward. The acceleration occurs because the net force (gravity minus any small air resistance) acts downward, doing positive work on the carriage. Near the bottom, the brakes exert a large resistive force opposite to the motion; the carriage does negative work against this force. The kinetic energy that has built up is then dissipated as heat and other thermal energy in the brakes and surrounding air, bringing the carriage to rest.
Examiner tips
- Mention GPE at the top and its conversion to KE during free fall.
- Explain that the downward net force (gravity) does work, causing acceleration.
- State that brakes do negative work, converting KE into heat.
- Show the final energy is lost as thermal energy, stopping the carriage.
Common mistakes
- Forgetting to mention the resistive work done by the brakes.
- Confusing the direction of work (positive vs negative) with the resistive force.
- Not specifying that the final energy is dissipated as heat rather than remaining as KE.
Mark scheme (5 marks)
- The carriage has gravitational potential energy (GPE) at the top of the tower
- As the carriage falls, GPE is transferred to kinetic energy (KE)
- The carriage speeds up because the net / resultant force acts downward (or because work is done by gravity)
- The brakes apply a resistive force, so the carriage does work against the resistive force
- The kinetic energy is dissipated as heat / thermal energy to the surroundings, so the carriage comes to rest
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 →