Given below are-a few situations

Given below are-a few situations, study them and state in which of the given cases work is said to be done. Give reason for your answer.
(i) A person pushing hard a huge rock but the rock does not move.
(ii) A bullock pulling a cart up to 1 km on road.
(iii) A girl pulling a trolley for about 2 m distance.
(iv) A person standing with a heavy bag on his " head.

(i) As the displacement is zero in 1st case.
So, work done = zero.
(ii) The work done in pulling a cart by the bullock will be +ve. As A and s are in same direction.
(iii) Work done in case of pulling a trolley by the girl will be +ve. As force and displacement are in same direction.
(iv) As there is no displacement, so work done by a person standing with a heavy bag on his head is zero.