An object is thrown vertically up. It reaches the highest point and then comes down. The work done by the force of gravity on the object is:

negative for the way up and positive for the way down

Reason — As, work done by an object is given by

W = FS cos θ

where,

• F is magnitude of force,
• S is magnitude of displacement, and
• cos θ is cosine of the angle θ between the directions of force F and displacement S .

Case 1 : When the object is thrown vertically up

When an object is thrown upwards then the displacement (upward) is opposite to the direction of force of gravity (downwards) i.e., θ = 180° so the work done on the body by the force of gravity is negative.

Case 2 : When the object is falling vertically down

When the object comes down, the force of gravity (downwards) is in the direction of displacement (downwards) i.e., θ = 0° and the work done by the force of gravity is positive.