AQA GCSE Physics: Energy

A child on a swing is pulled back and released from rest. The swing rises and falls repeatedly, but each successive swing reaches a slightly lower height than the one before, until eventually the swing comes to rest.

Describe and explain the energy transfers that take place during one swing (from the highest point on one side, through the lowest point, to the highest point on the other side), and explain why each swing reaches a lower height than the last. Refer to the principle of conservation of energy in your answer. (6 marks)

A ball of mass 0.60 kg is held at rest at a height of 1.8 m above the ground. It is then released and falls freely. Air resistance is negligible. Take the gravitational field strength as $g = 9.8\ \text{N/kg}$g=9.8 N/kg.

(a) Calculate the energy in the gravitational potential energy store of the ball at the moment it is released. Use $E_p = mgh$Ep​=mgh. Show your working and give the unit. (2 marks)

(b) Assuming all of this energy is transferred to the kinetic energy store, calculate the speed of the ball just before it hits the ground. Use $E_k = \tfrac{1}{2}mv^2$Ek​=21​mv2. (2 marks)

An electric kettle is rated at 2300 W. It transfers 460 000 J of energy to the water inside it.

(a) Calculate the time taken for the kettle to transfer this energy. Use $P = \dfrac{E}{t}$P=tE​. Show your working and give the unit. (2 marks)

(b) Of the 460 000 J transferred, 414 000 J usefully heats the water. Calculate the efficiency of the kettle. (1 mark)

A removal worker pushes a heavy crate 4.0 m across a level floor by applying a steady horizontal force of 250 N in the direction of motion.

(a) Calculate the work done by the worker on the crate. Use $W = Fs$W=Fs. (2 marks)

(b) The crate moves at a constant velocity. State what this tells you about the size of the friction force acting on the crate, and give a reason. (1 mark)

A country is deciding whether to build a new wind farm or a new gas-fired power station to generate electricity.

Give one advantage and one disadvantage of using wind rather than burning natural gas to generate electricity. (2 marks)

When energy is transferred, some is often dissipated to the surroundings.

Name the energy store that this dissipated (wasted) energy is usually transferred to. (1 mark)