Work, potential and kinetic energy — GCSE Physics practice questions

Question 1

A hiker carries a rucksack from a valley up to a mountain hut and puts it down on the floor of the hut.

Which energy store of the rucksack is greater at the hut than in the valley?

Accepted Answer

C: gravitational potential. The rucksack is higher at the hut than in the valley, so its gravitational potential energy store has increased. It is at rest in both places, so its kinetic store is the same (zero).

Question 2

A hailstone has a mass of 5.0 g. Just before it hits the ground it has 0.64 J of kinetic energy.

What is the speed of the hailstone?

Accepted Answer

C: 16 m / s. v = √(2 E_k / m) = √(2 × 0.64 / 0.0050) = √256 = 16 m / s. The mass must be in kilograms for the answer to be in m / s.

Question 3

A skier of mass 70 kg passes point X at a speed of 6.0 m / s. She skis down the slope to point Y, which is 25 m vertically below X, and passes Y at a speed of 18 m / s.

How much energy is transferred to the surroundings by friction and air resistance between X and Y? (g = 9.8 N / kg)

Accepted Answer

C: 7.1 kJ. At X: E_k = ½ × 70 × 6.0² = 1260 J. GPE lost = 70 × 9.8 × 25 = 17 150 J. At Y: E_k = ½ × 70 × 18² = 11 340 J. Energy dissipated = 1260 + 17 150 − 11 340 = 7070 J ≈ 7.1 kJ, transferred to the thermal store of the snow and the air.