Question

From the following activities find out whether work is positive, negative or zero. Give reasons for your

(a) A boy is swimming in a pond. 

(b) A coolie is standing with a load on his head. 

(c) Stopping a moving car by applying brakes. 

(d) Catching the ball which you friend has thrown towards you.

Answer 1

(a) A boy is swimming in a pond: The work done is positive because the direction of applied force and displacement are the same. 

(b) A coolie is standing with a load on his head: The work done is zero because the applied force does not cause any displacement. 

(c) Stopping a moving car by applying brakes: The work done is negative because the fore applied by the brakes acts in a direction opposite to the direction of motion of car. 

(d) Catching the ball which you friend has thrown towards you : Negative work because the force required to stop the ball, acts opposite to the displacement of the ball.