1. 1
   A washing machine motor is supplied with 5000 J of electrical energy during part of a wash cycle. Of this, 3500 J is usefully transferred to the kinetic energy store of the rotating drum, with the rest transferred to the thermal energy store of the surroundings by heating.

   (a)

   Which equation should be used to calculate the efficiency of the washing machine motor?

   [1 mark]

   • Aefficiency = useful energy output ÷ total energy output × 100%
   • Befficiency = total energy output ÷ useful energy output × 100%
   • Cefficiency = useful energy output × total energy output
   • Defficiency = useful energy output − total energy output

   (b)

   Which energy store does the wasted energy from the motor end up in?

   [1 mark]

   • AThe kinetic energy store of the drum
   • BThe thermal energy store of the surroundings
   • CThe chemical energy store of the water
   • DThe gravitational potential energy store of the machine

   (c)

   Calculate the efficiency of the washing machine motor.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A warehouse worker pushes a loaded trolley, applying a steady force of 60 N to move it a distance of 15 m across a flat floor.

   (a)

   Calculate the work done by the worker in pushing the trolley.

   [1 mark]

   • A4 J
   • B0.25 J
   • C900 J
   • D75 J

   (b)

   What does the work done by the worker equal, according to the principle of conservation of energy?

   [1 mark]

   • AThe power developed by the worker
   • BThe weight of the trolley
   • CThe distance moved by the trolley
   • DThe energy transferred to the trolley

   (c)

   The push takes 12 s. Calculate the power developed by the worker.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A construction crane's safety mechanism fails, allowing a steel beam of mass 400 kg to fall freely from rest through a height of 5 m before an emergency brake engages. Assume no air resistance.

   (a)

   Calculate the loss in gravitational potential energy of the beam as it falls the 5 m, taking g = 10 N/kg.

   [3 marks]

   (b)

   Assuming all the lost gravitational potential energy is transferred to the beam's kinetic energy store, calculate the speed of the beam just before the brake engages.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hiker climbs a hill, carrying a backpack, so that her body and backpack together (total mass 65 kg) rise through a vertical height of 250 m during a 3000 s walk. Her body supplies about 800 000 J of chemical energy from food to complete the climb.

   (a)

   Calculate the work done against gravity by the hiker in climbing the hill, and the useful power she develops during the climb, taking g = 10 N/kg.

   [6 marks]

   (b)

   Calculate the efficiency of the hiker's body at transferring the 800 000 J of chemical energy into the useful gravitational potential energy calculated in part (a), and describe, in terms of energy stores, where most of the rest of the energy is transferred to.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A gas-fired power station burns fuel that supplies 8000 J of chemical energy per second to a boiler. Of this, 3200 J per second is usefully transferred to electricity, with most of the rest wasted as heat carried away by cooling towers.

   (a)

   Calculate the efficiency of the power station.

   [1 mark]

   • A25.6%
   • B40%
   • C2.5%
   • D80%

   (b)

   Which method of thermal energy transfer is mainly responsible for the wasted heat carried away by the cooling towers?

   [1 mark]

   • AConvection
   • BConduction
   • CRadiation only
   • DSound

   (c)

   Calculate the amount of energy wasted per second by the power station.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A weightlifter raises a barbell of weight 800 N through a vertical distance of 2 m.

   (a)

   Calculate the work done by the weightlifter in raising the barbell.

   [1 mark]

   • A400 J
   • B1.6 J
   • C800 J
   • D1600 J

   (b)

   Which of the following correctly states what happens to the barbell's energy stores as it is raised?

   [1 mark]

   • AIts kinetic energy store increases and its gravitational potential energy store stays the same
   • BIts chemical energy store increases
   • CIts gravitational potential energy store increases
   • DIts thermal energy store increases

   (c)

   The lift takes 0.8 s. Calculate the power developed by the weightlifter.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A wrecking ball of mass 800 kg is released from rest and swings down on a cable, falling through a vertical height of 3.2 m before striking a wall. Assume all the lost gravitational potential energy is transferred to kinetic energy, with no air resistance.

   (a)

   Calculate the loss in gravitational potential energy of the wrecking ball as it falls the 3.2 m, taking g = 10 N/kg.

   [3 marks]

   (b)

   Calculate the speed of the wrecking ball just before it strikes the wall.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A solar-powered water pump lifts water from a well. The solar panel supplies 600 W of power to the pump. The pump uses this to lift water of total weight 3000 N through a vertical height of 1.5 m every 10 s.

   (a)

   Calculate the useful power output of the pump, and hence calculate the efficiency of the solar pump system, given the solar panel supplies 600 W.

   [6 marks]

   (b)

   Describe the energy transfers taking place, from the solar panel absorbing sunlight through to the water being raised, naming the energy stores involved at each stage, and suggest one reason the system is not 100% efficient.

   [6 marks]

   Total for question 8: 12 marks

End of questions