Final answer:
In both situations, the key concept at play is impulse. In a car collision, the force exerted on the occupant is spread out over a longer period of time, reducing the average force. Stopping a cannonball would also require exerting a force for a longer time.
Step-by-step explanation:
In both situations, the key concept at play is impulse. Impulse is the change in momentum of an object, and it is equal to the force applied to an object multiplied by the time interval over which the force is applied.
In the case of a car collision, when the car comes to a stop, the force exerted on the occupant is spread out over a longer period of time. This reduces the average force experienced by the occupant, providing a longer time interval for the change in momentum to occur.
In the case of stopping a cannonball, if you were to somehow stop it, you would also need to exert a force on it for a longer period of time to reduce the force experienced.