(a) Work done is positive, when a force acts in the direction of motion of the body.

For e.g. kicking a football

(b) Work done is negative, when a force acts opposite to the direction of motion of the body

For e.g. when a body is being lifted in the upward direction

(c) Work done is zero when a force acts at right angles to the direction of motion of the body

For e.g. No work is done by the porter in carrying the load.