OCR GCSE Physics: Energy

A ball is dropped from a height onto a hard floor. It bounces several times, and each bounce reaches a slightly lower height than the one before, until eventually the ball stops bouncing and rests on the floor.

Describe and explain the energy transfers that take place as the ball falls, hits the floor and bounces back up, and explain why each bounce is lower than the last. Refer to the principle of conservation of energy and to energy stores in your answer. (6 marks)

A stone of mass 2.0 kg is held at rest at a height of 5.0 m above the ground and then released. Air resistance is negligible. Take the gravitational field strength as $g = 10\ \text{N/kg}$g=10 N/kg.

(a) Calculate the energy in the gravitational potential store of the stone 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 store, calculate the speed of the stone just before it hits the ground. Use $E_k = \dfrac{1}{2}mv^2$Ek​=21​mv2. (2 marks)

A warehouse worker pushes a loaded trolley along a level floor, applying a steady horizontal force of 300 N in the direction of motion. The trolley moves 8.0 m.

(a) Calculate the work done by the worker on the trolley. Use $W = Fd$W=Fd. Show your working and give the unit. (2 marks)

(b) The worker does this work in a time of 6.0 s. Calculate the power developed. Use $P = \dfrac{E}{t}$P=tE​. (1 mark)

A toy launcher fires a small ball using a stretched spring. The spring has a spring constant of $200\ \text{N/m}$200 N/m and is stretched (extended) by 0.15 m before release.

(a) Calculate the energy stored in the elastic potential store of the stretched spring. Use $E_e = \dfrac{1}{2}ke^2$Ee​=21​ke2, where $k$k is the spring constant and $e$e is the extension. Show your working and give the unit. (2 marks)

(b) When the launcher fires, only 1.8 J is transferred to the kinetic store of the ball. Calculate the efficiency of the launcher. (1 mark)

On a cold day, a homeowner wants to reduce the rate at which their house loses energy to the surroundings. They decide to fit loft (roof) insulation made of a thick layer of glass wool.

Explain how loft insulation reduces the rate of energy transfer out of the house. Refer to conduction in your answer. (2 marks)

A moving car brakes and comes to a stop. The car's brakes get hot.

Name the energy store that the car's kinetic energy is mainly transferred to as it brakes to a stop. (1 mark)