question_answer

Explain with reason whether the potential energy in the following cases increases or decreases: (a) a spring is compressed, (b) a spring is stretched, (c) two dis-similar charges are brought near each other, (d) a body is taken away against the gravitational force, (e) air bubble rises up in water.

Answer:

                (a) When a spring is compressed, work is done on the spring in compressing it. Therefore, RE. increases. (b) When a spring is stretched, work is done on the spring in stretching it. Therefore, RE. increases. (c) Two dissimilar charges attract each other and come closer. Work is done by the field. Therefore, RE. decreases. (d) Work is done by us in taking the body away against the gravitational force. Therefore, P.E. increases. (e) Air bubble rises up in water because of upthrust. Therefore, RE. decreases.