 So Alice's car is seven meters long, and the fastest anything can travel is the speed of light. So the soonest the back of the car can break or come to a halt is in some time t equals seven over c. OK, so just at the point of impact, there is four and a half meters of Alice's car sticking up the back of the garage. In the time it takes for the shock waves to reach the back of the car, how far will the garage travel?