6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
A loft (roof space) in a house loses a lot of thermal energy in winter. A builder fits a thick layer of fibreglass insulation across the loft floor. Fibreglass is a thick mat of glass fibres that traps many small pockets of air.
Explain how the thickness and the thermal conductivity of an insulating material affect the rate at which energy is transferred through it, and explain why the trapped air in the fibreglass helps to reduce energy loss from the house. (6 marks)
A student investigated the specific heat capacity of aluminium using a solid aluminium block of mass 0.80 kg fitted with an electric heater. The heater transferred 24 000 J of energy to the block, and the temperature of the block rose from 18 °C to 51 °C.
(a) Calculate the change in temperature of the block. (1 mark)
(b) Using your answer to part (a), calculate the specific heat capacity of aluminium. Use the equation E=mcΔθ. Show your working and give the unit. (3 marks)
A roller-coaster car of total mass 500 kg is at rest at the top of the first hill, 35 m above the lowest point of the track. Take the gravitational field strength g=9.8 N/kg.
(a) Calculate the gravitational potential energy stored in the car at the top of the hill, relative to the lowest point. Use Ep=mgh. (2 marks)
(b) As the car runs down to the lowest point, 10 % of this energy is transferred to the surroundings by friction and air resistance. Calculate the kinetic energy of the car at the lowest point. (1 mark)
An electric kettle has a power rating of 2400 W. It transfers 2400 J of energy every second to its heating element, but only some of this energy usefully heats the water.
(a) In 90 seconds, the kettle transfers a total of energy to the element. Calculate the total energy transferred in this time. Use E=Pt. (2 marks)
(b) Of this total energy, 194 400 J is transferred usefully to the water. Calculate the efficiency of the kettle as a percentage. (1 mark)
A car of mass 1200 kg is travelling along a straight, level road at a speed of 8 m/s.
Calculate the kinetic energy stored in the car. Use the equation Ek=21mv2. Show your working and give the unit. (2 marks)
Power is the rate at which energy is transferred.
Write down the equation that links power, energy transferred and time, using words or the correct symbols. (1 mark)