Question

when wiil the work done be negative?

Answer 1

The work done on the body is negative when direction of the force acting on the body is opposite to the displacement of the body.
             W=F.S.cos theata
             when F  is opp to S then theata=180
             W=FScos180
                  = -F.S
         EXAMPLE:
     When u lift a book,you exert an upward force on the book and the books displacement is upward, so the workdone by u on book is positive.But the work done by the gravitational force on book being lifted is negative because the downward gravitational force is opposite to upward displacement.