When is the work done by a force is positive and negative ?

Explanation

(i) If the force acts in the direction of displacement, then the work done by the force is positive.
Example : When a bullock pulls a cart, the cart moves in the direction of force.
(ii) If the force acts opposite to the direction of displacement, then the work done by the force is negative.
Example : When brakes are applied to a moving vehicle, the work done by the braking force is negative.