Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

At every point around the circle, the angle $\theta$ between the displacement vector and the direction of the tension is $90^{\circ}$. Therefore; $W = \int ~T~ds~cos(\theta)$ $W = \int ~T~ds~cos(90^{\circ})$ $W = \int ~T~ds~(0)$ $W = 0$ The work done by the tension is zero.