State the condition when the work done by a force is (i) positive, (ii) negative. Explain with the help of examples.

(i) When the displacement of the body is in the direction of force then the work done is said to be positive.

Therefore, W = F × S

Example - When a child pushes a toy table then the force applied by the child and the displacement of the table are in the same direction. So, work done is said to be positive.

(ii) When the displacement of the body is in opposite direction to the force applied then the work done is negative.

Therefore, W = – F × S

Example - When a ball is thrown upwards with a force, the balls moves to a height (h).

However, the displacement is opposite to the direction of force of gravity.

W = -mgh