Work, Energy & Power (Edexcel International AS 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.

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

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.

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

Determine the efficiency of the system.

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