Work, Energy & Power (Edexcel International A Level Physics)

The diagram shows a lift system for moving people up and down a tall building. There is a counterweight to balance the weight of the lift. An electric motor is used to raise and lower the lift.

Explain how the counterweight affects the amount of work required from the electric motor to raise the lift.

The electric motor raises the lift through a height of 40.0 m in a time of 30.0 s.

Show that the output power of the electric motor is about 12 kW. 

total mass of lift and people = 2250 kg    

mass of counterweight = 1300 kg

The electric motor dissipates energy to the surroundings at a rate of 3600 W.

Determine the efficiency of the electric motor.

Efficiency = .............................

The diagram shows a system used to move a stone block up a ramp. A team of people uses a rope to pull the block at a constant speed.

height of ramp = 4.35 m

angle of ramp to horizontal = 6.0°

mass of block = 2.10 × 10³ kg

speed of block up ramp = 0.450 m s^–1

total power of team = 6.25 kW

Show that the total force that the team exerts on the block is about 14 kN.

Determine the total work done by the team.

Total work done = ...........................................

Show that the useful work done on the block is about 90 kJ.

Determine the efficiency of the system.

Efficiency = ........................................