A-Level Kinematics of uniform circular motion and centripetal acceleration: worked solution

Question

For a car travelling at constant speed around a horizontal circular path: explain why a resultant force acts on the car while it turns, and why this force does not change its kinetic energy.

As the car moves round the circle its velocity continually changes direction, so even at constant speed it is accelerating (centripetal acceleration directed towards the centre). By Newton's second law a resultant force is required to produce this acceleration, directed towards the centre of the circle. This centripetal force is always perpendicular to the car's velocity (and its displacement), so it does no work on the car. Since no work is done, the car's kinetic energy (and speed) stays constant.