1. 1
   A cyclist rides to the top of a hill, then stops pedalling and free-wheels down the other side, gradually speeding up as they descend, before finally applying the brakes to come to a stop at the bottom.

   (a)

   As the cyclist free-wheels down the hill, which energy store decreases while the kinetic energy store of the bicycle and cyclist increases?

   [1 mark]

   • AGravitational potential energy store
   • BChemical energy store
   • CElastic energy store
   • DNuclear energy store

   (b)

   When the cyclist applies the brakes to stop at the bottom of the hill, which two energy stores are directly involved in the transfer of energy at the brakes?

   [1 mark]

   • AKinetic energy store decreases, thermal energy store of the brakes increases
   • BGravitational potential energy store decreases, chemical energy store increases
   • CKinetic energy store increases, elastic energy store decreases
   • DChemical energy store decreases, nuclear energy store increases

   (c)

   Describe the energy transfers that take place from the moment the cyclist begins free-wheeling at the top of the hill to the moment they come to a complete stop at the bottom, referring to the principle of conservation of energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A household kettle is tested by an appliance manufacturer. For every 1000 J of total electrical energy supplied to the kettle, 800 J is usefully transferred to heat the water, while the rest is wasted, mostly as heat lost to the surrounding air through the kettle's casing.

   (a)

   A household kettle transfers 800 J of useful energy to heat the water for every 1000 J of total energy supplied to it. Calculate the efficiency of the kettle.

   [1 mark]

   • A80%
   • B125%
   • C20%
   • D8%

   (b)

   What happens to the 200 J of energy that is not usefully transferred to the water?

   [1 mark]

   • AIt is stored permanently inside the kettle's heating element
   • BIt disappears and is no longer part of the system
   • CIt is wasted, mainly transferred to the thermal energy store of the surroundings
   • DIt is converted entirely into sound energy

   (c)

   Suggest one design improvement the manufacturer could make to the kettle to increase its efficiency, and explain how this improvement would reduce the amount of wasted energy.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A homeowner living in a hot climate decides to repaint the roof of their house, changing it from a dark colour to white, in an attempt to keep the inside of the house cooler during the day without using more air conditioning.

   (a)

   A homeowner in a hot climate paints the roof of their house white instead of its original dark colour. Explain, in terms of the emission and absorption of radiation, why this change is likely to keep the inside of the house cooler during the day.

   [3 marks]

   (b)

   The homeowner also considers adding a layer of insulating material to the walls and roof space of the house. Describe how conduction, convection and radiation each contribute to unwanted thermal energy transfer into the house, and explain how insulation can reduce the effect of each process.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A factory installs a large electric motor that lifts heavy loads from ground level up to a storage platform. Engineers observe that, for every 100 J of electrical energy supplied to the motor, only 75 J is usefully transferred to the gravitational potential energy store of the load, with the rest being wasted, mainly as heat due to friction in the motor's moving parts and electrical resistance in its wiring.

   (a)

   Describe the energy transfers that take place as the motor lifts a load, and explain, using a Sankey diagram description in words, how such a diagram could represent these transfers.

   [6 marks]

   (b)

   The factory's engineers propose two possible improvements: lubricating the motor's moving parts to reduce friction, or replacing the motor's wiring with thicker cables to reduce electrical resistance. Evaluate which improvement is likely to have the greater effect on the motor's overall efficiency, and explain how each proposed change would reduce unwanted energy transfers.

   [6 marks]

   Total for question 4: 12 marks

End of questions