AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2022: Question 3

✅ Correct answers

• Child: gravitational potential energy decreases.
• Child: kinetic energy increases and then decreases to zero at position B.
• Springs: elastic potential energy increases.
• Surroundings: internal/thermal energy store increases (energy is dissipated).

💡 Key knowledge

• At the top, the child has the most gravitational potential energy.
• As the child falls, that energy is transferred into kinetic energy.
• When the trampoline stretches, the springs store more elastic potential energy.
• Some energy is wasted to the surroundings as thermal energy due to friction and air resistance.

🧠 Exam technique

• Use the exact language of energy stores.
• For 4 marks, one clear point is needed for each of: child, springs, surroundings.
• It is fine to say energy is “dissipated” for the surroundings.

❌ Common errors

• Saying the child’s kinetic energy only increases — it must then decrease to zero at the lowest point.
• Talking about “energy transferred” without naming the store.
• Saying the springs have kinetic energy — the mark scheme wants elastic potential energy.
• Ignoring the surroundings: this lost mark is common.

📐 Calculations — step by step

1. Use the elastic potential energy equation:
   E = 0.5 × k × e²
2. Find the spring constant, k, using position A:
   4.9 = 0.5 × k × 0.056²
3. Rearrange:
   k = (2 × 4.9) / 0.056²
4. Calculate k:
   k = 9.8 / 0.003136 = 3125 N/m
5. Use position B energy:
   8.1 = 0.5 × 3125 × e²
6. Rearrange for e:
   e² = (2 × 8.1) / 3125 = 0.005184
7. Square root:
   e = √0.005184 = 0.072 m

Extension = 0.072 m

✅ Correct answer

Extension of each spring at position B = 0.072 m

This matches the mark scheme answer. Full marks come from showing the substitution, rearrangement, and final value with the correct unit.

💡 Key knowledge

• Elastic potential energy depends on extension.
• The equation is E = 0.5 × k × e² .
• k is the spring constant in N/m.
• e is the extension in m.

🧠 Exam technique

• Use the values from position A to find k first.
• Then use the value at position B to find the new extension.
• Write units clearly. Final answer must be in metres.
• Show every rearrangement step for method marks.

❌ Common calculation traps

• Forgetting the 0.5 in the equation.
• Using 4.9 J directly for position B instead of the updated 8.1 J.
• Mixing up extension and total length.
• Leaving the answer in cm or forgetting the unit.
• Not squaring the extension before rearranging.

✅ What distinguished top answers

• They used the equation correctly and rearranged it neatly.
• They showed the working for k and then for e .
• They gave a final answer rounded sensibly to 0.072 m.

✅ Correct answer

The total energy transferred by the child

💡 Key knowledge

• Work done is the same as energy transferred.
• In this question, the child transfers energy to the trampoline and surroundings.

🧠 Exam technique

• This is a tick box question: only one option is correct.
• Choose the response that matches the definition of work done most closely: energy transferred.

❌ Common errors

• Choosing the average force or maximum force — these are not what work done equals.
• Picking “total energy store of the child” — work done is about transfer, not just the store.

✅ Remember these facts

• Gravitational potential energy decreases as the child falls.
• Kinetic energy increases then falls to zero at the lowest point.
• Elastic potential energy in the springs increases.
• Some energy is dissipated to the surroundings as thermal energy.
• Use E = 0.5 × k × e² for elastic energy.

🧠 Final exam tip

GCSE energy questions often reward clear store names and step-by-step calculations. If you name the stores accurately and show your working with units, you are much more likely to secure full marks.