An electric motor lifts a box of mass 12 kg through a vertical height of 3.0 m.
Gravitational field strength = 10 N/kg
Use the equation: gravitational potential energy=mass×gravitational field strength×height\text{gravitational potential energy} = \text{mass} \times \text{gravitational field strength} \times \text{height}gravitational potential energy=mass×gravitational field strength×height
Calculate the energy transferred to the gravitational potential energy store of the box.
The motor is supplied with 0.60 kJ of energy to lift the box.
Calculate the efficiency of the motor.
Give your answer as a percentage.
Explain why the efficiency of the motor is less than 100%.
50 exam-style questions on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one has a worked solution and a mark scheme showing where the marks go.