Answer :
When the object moves in the opposite direction of the force acting on it, the work done by the force on the object is negative. For example, when we through a ball upward, during the upward motion of the ball, the gravitational force acts downward, but it moves upward. So the work done by gravity on the ball is negative.
When an object moves in the opposite to the direction of force it is called as work done in negative . eg when you swim your force is acting backwards but your moving forward so work done is negative.