Q1. When do we say that work is done? [NCERT]
Ans.Work is said to be done by a force acting on the object when the object is displaced along the direction of force. For example,
(i) A girl pulls a trolley and the trolley moves through a distance. The girl has exerted a force on the trolley and it is displaced along the direction of force. Therefore, work is done.
(ii) Lift a book through a height. To do this, you must apply a force. The hook rises up. There is a force applied on the book and the book has moved up in the direction of force. Hence, work is done. Thus, following two conditions need to be satisfied for work to be done: a, force should act on an object, and
(iii) the object must be displaced along the direction of force.