Question

why are cool it does not work when he moves on a level road while carrying a box on his head?

Answer 1

1. Work done by a coolie, walking on level road with load on his head, on the load is zero.

2. Work done = Force x displacement

W = F.s = Fs cos θ

where  θ is the angle between the direction of force and the direction of displacement of the object. If they are perpendicular to each other  θ = 90°. We have cos  90° = 0. Therefore

W  = Fxsx0 = 0