Power and efficiencyEdexcel A-Level Physics: Mind map

Exam questions on Power and efficiency

1. A motor in a building site hoist lifts a load of mass 250 kg through a height of 12 m at constant speed in 30 s. The electrical power supplied to the motor during the lift is 1.4 kW. Take g = 9.81 N kg⁻¹.
   Calculate the energy wasted by the motor during the lift.2 marks
2. A householder compares two lamps that both give 3.0 W of light output. The filament lamp has an input power of 60 W. The LED lamp has an input power of 9.0 W.
   The householder replaces a filament lamp with the LED lamp and uses it for 1000 hours. Calculate the energy saved, in joules.2 marks
3. A cyclist, with a bicycle, has a total mass of 85 kg and rides at a steady 4.0 m s⁻¹ up a road that rises 6.0 m for every 100 m travelled along the road. Resistive forces may be ignored. Take g = 9.81 N kg⁻¹.
   Calculate the useful power the cyclist must produce to raise herself and her bicycle up the road.3 marks