OCR GCSE Combined Science: Physics: Energy

A homeowner wants to reduce the rate at which their house loses thermal energy so that it stays warmer for longer and costs less to heat.

Explain, using ideas about thermal energy transfer, how measures such as loft insulation, double glazing and thick walls / cavity wall insulation reduce the rate of energy loss from a house. In your answer refer to how the thermal conductivity and thickness of a material affect the rate of energy transfer. (6 marks)

A car of mass 1500 kg is travelling in a straight line at a velocity of 20 m/s.

(a) Calculate the kinetic energy of the car. Use $E_k = \dfrac{1}{2}mv^2$Ek​=21​mv2. Show your working and give the unit. (3 marks)

(b) The car then doubles its speed to $40\ \text{m/s}$40 m/s. State, with a reason, how many times greater its kinetic energy becomes. (1 mark)

A student of mass 60 kg climbs a flight of stairs, rising a vertical height of 1.5 m. The gravitational field strength is $10\ \text{N/kg}$10 N/kg.

(a) Calculate the gain in gravitational potential energy of the student. Use $E_p = mgh$Ep​=mgh. Show your working and give the unit. (2 marks)

(b) State the energy store that this gravitational potential energy was transferred from. (1 mark)

A worker pushes a heavy crate along a warehouse floor. The worker applies a horizontal force of 250 N and moves the crate a distance of 8.0 m in the direction of the force.

Calculate the work done by the worker on the crate. Use $W = Fs$W=Fs. Show your working and give the unit. (3 marks)

An electric motor is supplied with 200 J of energy every second. Of this, only 60 J is transferred usefully to the kinetic energy store of a load; the rest is transferred to the surroundings by heating.

Calculate the efficiency of the motor. Use $\text{efficiency} = \dfrac{\text{useful energy transferred}}{\text{total energy supplied}}$efficiency=total energy supplieduseful energy transferred​. Give your answer as a percentage. (2 marks)

A ball is dropped and falls freely towards the ground. Air resistance is negligible.

State the main energy transfer that takes place as the ball falls. (1 mark)