Question

Give example of a situation in which an applied force does not result in a change in kinetic energy.

Answer 1

i) Let a ball tied to a string and is moving in a vertical circle. At any instant of time the displacement is tangential, and the tension is central in nature, i.e., tension in the string and the small displacement at any instant are perpendicular to each other.

ii) Similarly, a ball tied to a string and is moving in a horizontal circle.

Hence, work done by tension force will be zero and according to work energy theorem tension force will not cause any change in kinetic energy of ball.

iii) Similarly, work done by gravity when a ball is tied to a string and is moving in a horizontal circle.

Final answer: work done by tension when a body tied with string moving in a vertical circle, horizontal circle, work done by gravity when a ball is tied to a string and is moving in a horizontal circle etc.