The crane shown in the figure lifts its 500N load to the top of the building from A to B. Distances are as shown on the diagram. Calculate how much work is done by the crane.

Question 4

The crane shown in the figure lifts its 500N load to the top of the building from A to B. Distances are as shown on the diagram. Calculate how much work is done by the crane.

The dotted line shows the track of the load as it is lifted by the crane.

Reference: Cambridge International AS and A Level Physics Coursebook – 2^nd edition – by Sang, D., Jones, G., Woodside, R. and Chadha, G.

Solution:

Work done = Force × Displacement in direction of the force

The load is first lifted vertically from A to a height of 40 m (the height of the building). It is moved (horizontally from that position to point B)

To lift load vertically (an upward force is required) from A to a height of 40 m,

Work done = 500 × 40 = 20 000 J

Now, to keep the load at this position, an upward force is still needed. But now, the load is moved horizontally. So, work done for this movement is ZERO since the force is vertical while the displacement is horizontal [there is no component of displacement in the direction of the force].

Work done by the crane = 20 000 J = 20 kJ