Notice that the car is not in oscillation in this problem. We can, however, model the system as an object attached to a spring, with the object being the automobile. Imagine a cart on an air track with a stiff spring extending from one end. When the cart hits the end of the air track, we could investigate how much the spring compresses before the cart stops. That's the same problem as the one we have here. We'll use m for the mass of the car, k for the force constant, and x for the distance the spring compresses