Question

When a porter moves on a railway platform, the work done on the load on his head is zero because the force applied on the load is in the upward direction but displacement it is in the horizontal direction. However the Porter is applying a force on the ground to move forwards, taking the load as a part of the Porter (since it touches him )the work done shouldn't be zero. Please explain the flaw in my concept in detail.

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 according to physics workdone is zero but according to biology there is workdone due to muscles. thats why there is the pain in the body of workers. hope u like it