Past exam of the short options paper of the physics Prelims of the University of Oxford / 2021 / S03 / 3 / a / Solution

For a particle on a circle, the tangential speed is $v=r\dot{\varphi }$, the moment of inertia is $I=m{r}^2$, and the angular momentum is $L=I\dot{\varphi }=mrv$. Hence its kinetic energy isThere is no potential energy variation along the circle in the stated model.