Describe — 5 marks
A student is making a cup of hot tea. She pours boiling water from a kettle into a ceramic mug. The mug becomes warm to touch, and the temperature of the water gradually decreases over time.
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(a) Describe the energy transfer that occurs when the hot water is poured into the mug.
[2 marks]
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(b) Describe what happens to the thermal energy of the water as it cools down in the mug.
[2 marks]
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(c) Describe how the mug could be designed to reduce the rate of energy transfer to the surroundings.
[1 mark]
Show mark scheme
- (a) Thermal energy is transferred from the hot water to the ceramic mug / surroundings. (1 mark)
- (a) This occurs through conduction / heat conduction through the ceramic material. (1 mark)
- (b) The thermal energy of the water decreases over time. (1 mark)
- (b) Energy is transferred to the surroundings / air around the mug through conduction and radiation. (1 mark)
- (c) Use insulating materials / double walls with air gap / add a lid to reduce heat loss to surroundings. (1 mark)
Suggest — 4 marks
A student sets up an experiment to investigate energy transfers in a simple pulley system. A 2 kg mass is attached to a string that passes over a pulley and is pulled upward by hand. As the mass is lifted 0.5 m at a constant velocity, the student measures that 15 J of energy is supplied by the person pulling the string. The gravitational potential energy gained by the mass is calculated to be 10 J (using g = 10 m/s²).
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(a) Calculate the efficiency of the pulley system.
[1 mark]
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(b) Suggest where the 5 J of energy that was not stored as gravitational potential energy has been transferred to. Explain your answer.
[2 marks]
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(c) Suggest two practical modifications that could be made to the pulley system to improve its efficiency. For each suggestion, explain how your modification would reduce energy loss.
[1 mark]
Show mark scheme
- (a) Efficiency = (useful energy output / total energy input) × 100 = (10 / 15) × 100 = 66.7% (or 67% or 2/3)
- (b) The 5 J has been transferred to thermal energy / heat energy
- (b) Due to friction in the pulley system / friction between string and pulley / air resistance / friction at the pivot
- (c) Award 1 mark for any two distinct, justified suggestions. Each suggestion must include both the modification AND an explanation of how it reduces energy loss.
Calculate — 2 marks
An electric kettle has a power rating of 2000 W. It is switched on for 90 seconds to boil water.
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(a) Calculate the total energy transferred by the kettle.
[1 mark]
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(b) The kettle is 85% efficient. Calculate the useful energy transferred to the water.
[1 mark]
Show mark scheme
- (a) 180 000 J (accept 180 kJ)
- (b) 153 000 J (accept 153 kJ)
Explain — 3 marks
A student drops a rubber ball from a height of 1 metre. The ball bounces on the ground but does not return to its original height. The student notices that the ball and the ground feel slightly warmer after several bounces.
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(a) Explain the main energy transfer that occurs as the ball falls towards the ground.
[1 mark]
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(b) Explain why the ball does not bounce back to its original height of 1 metre.
[2 marks]
Show mark scheme
- (a) Gravitational potential energy decreases and kinetic energy increases
- (a) or gravitational potential energy is transferred to kinetic energy
- (b) Some energy is transferred to the surroundings
- (b) as thermal energy (and/or sound energy)
- (b) or not all kinetic energy is transferred back to gravitational potential energy
Evaluate — 3 marks
A student drops a rubber ball from a height of 1.0 m. The ball bounces on the floor and reaches a maximum height of 0.7 m on its first bounce. The student investigates the energy transfers that occur during this process.
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(a) State the energy store of the ball at its maximum height after bouncing.
[1 mark]
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(b) Evaluate why the ball does not reach its original height of 1.0 m when it bounces back up.
[2 marks]
Show mark scheme
- (a) Gravitational potential energy (GPE)
- (b) Some energy is transferred to the thermal energy store (of the ball/floor/surroundings)
- (b) Energy is also transferred to the kinetic energy store of the floor / energy is dissipated / work is done against air resistance
GCSE Perfect