Key facts

curriculum-key-fact
Work done has the same units as energy – joules, J. This is because energy is the ability to do work.
curriculum-key-fact
When work is done energy is transferred from one form to another.

You must have energy to do work.

A person could not push the box and do work in the example above without a store of energy.

The person transfers 20 J of energy in doing 20 J of work pushing the box.

Work done = Energy transferred.

Question

Calculate the work done by a crane when a mass of 200 kg is lifted 3 m vertically.

Calculate the work done by a crane when a mass of 200 kg is lifted 3 m vertically.

Upward force F = 2000 N

weight = mg

weight = 200 kg x 10 N/k

weight = 2000N.

Since the 200 kg object is being lifted vertically, the minimum upward force F equals the weight of the object.

Upward force F = 2000 N.

Work done W = Fd

F = 2000 N

d = 3 m

W = 2000 N x 3 m

W = 6000 J

The work done by the crane is 6000J.