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Let us compare three situations.
First, the car is at rest, not moving, has never been moving, and I apply
the brakes. Obviously I will feel nothing.
Second, the car has been moving but under the influence of gravity the car
and its contents have come instantaneously at rest. Call this time t=0. I
apply the brakes at this instant. Is there any physical difference between
the objects involved at this instant and the previously mentioned condition?
Answer-No. Therefore I should feel nothing at this time either..
Third the car has been moving under the influence of gravity, I do not apply
the brakes, the car and contents at some instant have a zero velocity and
then begin rolling backward, having at all time a constant acceleration, and
no jerk.