Question

A block of mass 30 kg is pulled up by a rope as shown in Fig. with a constant speed by applying a force of 200 N parallel to the slope. P and Q are the initial and the final positions of the block respectively. Calculate:

1. the work done by the force in moving the block from P to Q.
2. the potential energy gained by the block.
3. account for the difference in work done by the force and the increase in potential energy of the block.

Answer 1

Given: Mass of block, m = 30 kg

Applied force, F = 200 N

Distance along the slope, s = 3 m

Vertical height gained, h = 1.5 m

Taking, g = 10 m s⁻²

(a) Work done by the force 

W = F × s

= 200 × 3

= 600 J

(b) Potential energy gained by the block

PE = mgh

PE = 30 × 10 × 1.5

= 450 J

(c) Difference between work done and increase in potential energy 

W − ΔPE

600 − 450 = 150 J

This difference is the work done against friction between the block and the inclined surface. It is mainly converted into heat energy.