NumericalModerate1 mark
6(iii)
A ball of mass 20 g falls from a height of 45 m. It rebounds from the ground to a height of 40 m. Calculate :
initial potential energy of the ball.
Topic: Gravitational potential energy
Question wording verified against source paper
Answer
Exam answer
Given: mass m = 20 g = 0.02 kg, height h = 45 m, g = 10 m s⁻²
Potential energy = m g h = 0.02 × 10 × 45 = 9 J
Initial potential energy of the ball = 9 J
Explanation
Convert the mass to kilograms first. Using 20 g directly gives 9 000, which is not in joules — the SI unit of mass is the kilogram, and every mechanics formula assumes it.
Potential energy is measured from the ground here, so h is the full 45 m of the drop.
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