Question

A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done :
a) by the force applied by the boy?
b) by the gravitational force of earth ?

Answer 1

a) force applied by the boy is in the same direction that of displacement so work done is positive

b) when ball is moving upward gravitational force is in opposite direction of displacement so work done is negative.

But when ball falls back gravitational force is in the same direction as that of displacement so work done by gravity is positive