A bungee rope is used to store elastic potential energy during a jump. Explain how the energy stored in the bungee rope depends on whether the rope deforms elastically or plastically.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A bungee jumper falls and the bungee rope stretches. After the jump, the rope is inspected and found to have a permanent increase in length.
Model answer (4 marks)
1. If the rope deforms elastically it returns to its original length when the force is removed.
2. The work done on the rope is stored as elastic potential energy, U=½kx², and is fully recoverable.
3. If the rope deforms plastically it does not return to its original length – the deformation is permanent.
4. In plastic deformation part of the work is lost as heat or other forms, so less elastic potential energy is recovered by the jumper.
2. The work done on the rope is stored as elastic potential energy, U=½kx², and is fully recoverable.
3. If the rope deforms plastically it does not return to its original length – the deformation is permanent.
4. In plastic deformation part of the work is lost as heat or other forms, so less elastic potential energy is recovered by the jumper.
Examiner tips
- Use the definition of elastic vs plastic deformation first. Show the energy equation for elastic case. Explain loss of energy in plastic case. Keep answer to four clear points.
Common mistakes
- Confusing elastic potential energy with total work done. Forgetting to mention permanent deformation in plastic case. Using vague terms like "energy loss" without specifying heat or other forms.
Mark scheme (4 marks)
- Elastic deformation means the rope returns to its original shape/length when the force is removed
- The work done on the rope equals the elastic potential energy stored, provided the rope deforms elastically (does not exceed the elastic limit)
- Plastic deformation means the rope does not return to its original shape/length when the force is removed / the deformation is permanent
- If the rope deforms plastically, not all the elastic potential energy is recovered / some energy is transferred to other forms (e.g. thermal), so less energy is returned to the jumper
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Forces and elasticity questions
- Describe what happens to a spring when it is loaded with increasing force, from …
- A student presses down on a foam cushion and then removes the force. The foam re…
- A student stretches a rubber band and then releases it. The rubber band returns …
- Explain why a spring that has been stretched beyond its elastic limit will not r…