1. The problem statement, all variables and given/known data If only an external force can change the state of motion of a body, how can the internal force of the brakes bring a car to rest? 3. The attempt at a solution I think that it may be because friction between brakes and wheels converts kinetic energy into heat. Or perhaps friction between brakes and wheels somehow (?) leads to friction between wheels and the road, causing a retarding force. Thank you!