Question

If a person is carrying a load on his head and he walks upright and travels a lot distance and said his friend,"I have done a lot of work" but his friend said that scientifically he had not done any work. Explain why?​

Answer 1

Answer:

When the man lifts it vertically upwards. As in this case, he has to move vertically opposite to gravity

Explanation:

Work is done only to the extent that the direction of movement is aligned with the direction of force. That is, the dot product of force and displacement vectors. A load on his head would seem to be directed downwards (gravity)

W = FdcosΘ

So maximum work will be done when cosΘ has maximum value of | 1 |.

So the work done will be maximum if he lifts it at an angle of cos 180 (When the man lifts it vertically upwards) , where he has to do work not only against gravity but also value of cos Θ will be maximum |1|.