Question

A block A, whose weight is 100 N, is pulled up a slope of length 5 m by means of a constant force F (= 100 N) as illustrated in the following figure.

1. What is the work done by force F in moving block A, 5 m along the slope?
2. What is the increase in potential energy of the block A?
3. Account for the difference in work done by the force and the increase in potential energy of the block.

Answer 1

F = 100 N; S = 5 m

(a) Work done by the force F

W = F × S

= 100 × 5 = 500 J

(b) Increase in PE = mgh

= 100 × 3 = 300 J

(c) Difference in work = 500 – 300 = 200 J

This energy is used to work against the frictional force between the block and the slope of the plane, and it appears as heat.