Question

A motor is used to operate a lift. There is a man in the lift. The input power of the motor is 6200 watts. The lift and the man have a total mass of 580 kg. The lift moves up a distance of 12 m in 15 s. Calculate the tension in the cable when the lift is moving at constant speed.

Answer 1

Answer: 8500 N

Explanation:

You are given that the input power of the motor is 6200 watts

Since the man is in the lift, and the lift and the man have a total mass of 580 kg. The power 6200 watt is responsible to move up the lift and the man. Where power is the rate at which work is done. That is

Power = workdone/ time

But workdone = force × distance

Substitute that in power formula

Power = force × distance/time

But distance/time = velocity

Therefore, power is the product of force and velocity. That is,

P = FV

If the lift moves up a distance of 12 m in 15 s, then,

Velocity V = 12/15 = 0.8 m/s

Substitutes V and P into the power formula

6200 = F × 0.8

F = 6200/0.8

F = 8500 N

The calculated force is equal to the tension in the cable when the lift is moving at a constant speed.

Therefore, the tension in the cable is equal to 8500 N