A roller coaster car starts from rest at the top of a track and reaches the bottom of the track, moving at high speed. Describe the energy changes that take place as the car moves from the top to the bottom of the track. Include reference to any waste energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The car starts with high gravitational potential energy (GPE) and no kinetic energy (KE). As it moves down, GPE is converted into KE, so KE increases while GPE decreases. Some of the energy is lost as heat and sound due to friction between the car and the track and air resistance, so a small amount of energy is transferred to thermal energy. The total energy of the system remains constant – the loss in GPE plus the increase in KE plus the waste energy equals the initial total energy.
Examiner tips
- Use the terms ‘gravitational potential energy’, ‘kinetic energy’ and ‘thermal energy’.
- Show the energy flow: GPE → KE and GPE → thermal energy.
- Mention friction/air resistance as the source of waste energy.
- State that total energy is conserved.
Common mistakes
- Confusing potential energy with kinetic energy or vice versa.
- Omitting the waste energy (friction/air resistance).
- Not linking the energy changes to the conservation of energy principle.
Mark scheme (4 marks)
- Gravitational potential energy decreases / is transferred from the gravitational potential energy store
- Kinetic energy of the car increases / energy is transferred to the kinetic energy store
- Some energy is dissipated / transferred to the thermal energy store due to friction (between the car and the track / air resistance)
- Total energy is conserved / the total energy at the bottom equals the total energy at the top (linking to conservation of energy)
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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