Define work done.
From the list below, select the two quantities that are needed to calculate the power of a machine:
A crane at a construction site lifts 10 steel beams, each of mass 150 kg150\text{ kg}150 kg, through a vertical height of 60 m60\text{ m}60 m in a time of 45 s45\text{ s}45 s.
Calculate the useful power needed to lift the beams through this height. (State the value of ggg you use in your calculation.)
The crane is driven by an electric motor. State a reason, other than friction, why the total power supplied by the motor is greater than the useful power needed to lift the beams.
533 exam-style questions on CIE IGCSE Physics 1.7 Energy, work and power, covering 1.7.1a Energy stores and energy transfers, 1.7.1b Conservation of energy, 1.7.1c Kinetic and gravitational potential energy, 1.7.2 Work done, 1.7.3 Energy resources, 1.7.3a Energy resources and electricity generation, 1.7.3b Nuclear fusion as an energy source, 1.7.3c Efficiency of energy transfer, and 1.7.4 Power. Each one has a worked solution and a mark scheme showing where the marks go.