Positive and Negative Work

When you press the accelerator of the car, the force is in the direction of motion of the car. As a result, you increase the speed of the car. The work done is positive.

When you apply brakes of a car, the force is applied in a direction opposite to its motion. The car loses speed and may finally come to rest. Negative work is said to have been done.

In case the applied force and displacement are as right angles, i.e. θ = 90º, no work is said to be done.