AQA · GCSE · Physics · Higher

Calculating the Drone’s Lower Height

Q04.2 4 marks

When the drone reached a height of 840 m the motor was switched off. The motor was switched back on after a short time, when the drone had fallen to a lower height above the ground. The change in gravitational potential energy of the drone during the fall to this lower height was 3920 J. The mass of the drone is 2.5 kg.

gravitational field strength = 9.8 N/kg

Calculate the height above the ground of the drone when the motor was switched back on.

Use the Physics Equations Sheet.

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Marking points

1 Uses the gravitational potential energy equation with the supplied mass, field strength and energy change.
2 Correctly rearranges or otherwise progresses the equation to find the height change.
3 Obtains a fall in height of 160 m (or the equivalent final-energy value on the alternative route).
4 Gives a final height above ground of 680 m, allowing a consistent carried-forward value.

Full-mark answer

Use $\Delta E_p = mg\Delta h$ : $3920 = 2.5 \times 9.8 \times \Delta h$ , so $δ h = 3920/(2.5 × 9.8) = 160\ text{m}$. The drone fell from 840 m, so its height when the motor was switched back on was $840 - 160 = 680\ \text{m}$ .

Why this answer loses marks

Gives only the distance fallen.

The question asks for height above the ground, so subtract the fall from the starting height.

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