question_answer 54)

                  A body is being raised to a height h from the surface of earth. What is the sign of work done by                 (a) applied force                 (b) gravitational force                

Answer:

                  \[W=Fds\,\cos \theta \]                 Since the directions of the applied force and the displacement of the body are same, so \[\theta ={{0}^{o}}\]. Hence, work done is positive.                 On the other hand, the directions of gravitational force and the displacement of the body are opposite to each other. That is, \[\theta ={{180}^{o}}\]. Therefore, work done is negative.