Work and Energy and Circular motion.

Question

A stone swings on a horizontal circle at the end of a string 2.0 m long. The period of the motion is 1.2 s. How much work does the tension in the string do on the stone in .40 s?

I am having much trouble with circular motion. Is it possible you can explain mental processes as you choose what you do next?

Answer 1

The answer is zero work because the direction of the force associated with the tension is always perpendicular to the direction of motion.

Answer 2

If the length of the string does not change, the radius of the circle does not change. Then the tension does not do any work. In this problem, the tension changes the direction of motion (keeping the stone in a circular path), but it does no work if the radius of the circle does not change. In order to do work, there must be some displacement in the direction of the tension. But if the radius does not change, there is no displacement in that direction, and hence no work is done by the tension.

Where did this question come from?