Edexcel GCSE Physics: Conservation of Energy

A roller-coaster car starts from rest at the top of a high track and runs down to the bottom, where it is moving quickly. As it travels, some energy is also transferred to the surroundings because of friction and air resistance.

Describe and explain the energy transfers that take place as the car runs from the top of the track to the bottom. Your answer should refer to the principle of conservation of energy and explain what happens to the energy that is not transferred to the kinetic store. (6 marks)

A block of metal of mass 2.0 kg is heated by a small electric heater. The temperature of the block and the energy supplied are recorded.

Energy supplied / J	Temperature / °C
0	20
3600	30
7200	40
10800	50

(a) Determine the rise in temperature of the block when 7200 J of energy has been supplied. (1 mark)

(b) Calculate the specific heat capacity of the metal. Use $Q = mc\,\Delta\theta$Q=mcΔθ, rearranged as $c = \dfrac{Q}{m\,\Delta\theta}$c=mΔθQ​. Show your working and give the unit. (3 marks)

A car of mass 900 kg is travelling at a velocity of 20 m/s.

(a) Calculate the kinetic energy of the car. Use $E_k = \tfrac{1}{2}mv^2$Ek​=21​mv2. Show your working and give the unit. (2 marks)

(b) State what happens to most of this energy when the car brakes to a stop. (1 mark)

A worker lifts a box of weight 120 N vertically through a height of 1.5 m onto a shelf.

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

(b) State how much gravitational potential energy the box has gained. (1 mark)

An electric motor is supplied with 2000 J of energy. Of this, 1500 J is transferred usefully to lift a load; the rest is dissipated as thermal energy.

Calculate the efficiency of the motor. Use $\text{efficiency} = \dfrac{\text{useful energy output}}{\text{total energy input}}$efficiency=total energy inputuseful energy output​. (2 marks)

The principle of conservation of energy is one of the most important ideas in physics.

State the principle of conservation of energy. (1 mark)