AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2024: Question 4

✅ Correct answers

• Chemical store of energy decreases in the battery.
• Gravitational potential energy of the drone increases.

💡 Key knowledge

• A battery stores energy chemically.
• When the drone is rising, its height increases, so its gravitational potential energy increases.
• Because it moved at constant speed, its kinetic energy stayed the same.

🧠 Exam technique

• Use the exact energy-store names from GCSE Physics.
• If the question says “other changes”, do not repeat thermal energy.
• “Battery runs out” links directly to chemical store decreases.

❌ Common errors

• Saying kinetic energy increases even though the speed is constant.
• Writing only “energy increases” without naming the store.
• Confusing gravitational potential energy with “height” but not stating the energy store.

📐 Calculations: step-by-step

1. Use the equation: ΔE_p = m × g × Δh
2. Substitute the values: 3920 = 2.5 × 9.8 × Δh
3. Rearrange: Δh = 3920 ÷ (2.5 × 9.8)
4. Calculate the height fallen: Δh = 160 m
5. Find the new height: 840 − 160 = 680 m

✅ Correct answer

Height above ground = 680 m

This full-mark answer can be shown either by finding the change in height first, or by finding the final gravitational potential energy and then converting it back to height.

🧠 Exam technique

• Always use ΔE_p = mgh for a change in height.
• Keep units consistent: mass in kg, g in N/kg, height in m, energy in J.
• Show substitution clearly to secure method marks.
• If you get an answer from an alternative correct method, it can still score full marks if it is consistent.

❌ Common errors

• Using 840 m as the height in the equation instead of the height lost.
• Forgetting to subtract from 840 m at the end.
• Rearranging incorrectly and dividing by only one number instead of 2.5 × 9.8 .
• Leaving the answer as 160 m — that is the distance fallen, not the final height.

📐 Calculations: step-by-step

1. The drone had 150 J of kinetic energy when the motor was switched off.
2. It also lost 3920 J of gravitational potential energy during the fall.
3. So the maximum kinetic energy when the motor was switched back on is:
   4070 J = 3920 + 150
4. Use the kinetic energy equation:
   E_k = 0.5 × m × v²
5. Substitute the values:
   4070 = 0.5 × 2.5 × v²
6. Rearrange:
   v = √(4070 ÷ (0.5 × 2.5))
7. Calculate:
   v ≈ 57.1 m/s
8. Convert to km/s:
   57.1 m/s = 0.0571 km/s

✅ Correct answer

Maximum possible speed = 0.057 km/s

Equivalent values accepted: 57 m/s or 57.1 m/s before conversion.

🧠 Exam technique

• In “maximum possible speed” questions, assume the energy transfer is ideal unless told otherwise.
• Use the correct equation: E_k = 0.5mv² .
• Make sure you include the extra 150 J from the kinetic energy already present.
• Convert your final answer to the unit asked: km/s, not m/s.

❌ Common errors

• Using 3920 J only and forgetting the original 150 J.
• Getting v² but forgetting to square root.
• Leaving the answer in m/s when the question asks for km/s.
• Using the wrong formula, such as E_p = mgh .

💡 Key knowledge

• E_p = mgh
• E_k = 0.5mv²
• Energy in joules: J
• Mass in kilograms: kg
• g = 9.8 N/kg

🧠 How to get full marks

• State the equation first.
• Substitute numbers carefully.
• Show rearrangement.
• Finish with the answer and the correct unit.

❌ Calculation traps

• Forgetting the ×0.5 in kinetic energy.
• Using 840 m instead of the drop in height.
• Mixing up change in GPE with final GPE.
• Not converting to km/s at the end.