Question

Why does no work is done when a coolie lift luggage and move horizontally?

Answer 1

Remember the work done by an object and the work done on an object are not same they are diifferent from each other. Case 1: if a coolie walks on level road with load on his head he is moving himself and also he is moving the object. So to move him self on the level road he is applying force on himself to displace him so here he is doing wor which is equal to the product of the force applied and the displacement. He is moving the load on his head which alsready on his head so here is applying the force on the body to accelerate it. So the work done by him to move the load is equal to the change in the load's kinetic energy ( here is no change in potential energy as the height of the object is not changed