A small object with momentum 7.0 kg∙m/s approaches head-on a large object at rest. The small object bounces straight back with a momentum of magnitude 4.0 kg∙ m/s. What is the magnitude of the large object's momentum change?

The magnitude of the large object's momentum change is 3 kilogram-meters per second.

Explanation:

Under the assumption that no external forces are exerted on both the small object and the big object, whose situation is described by the Principle of Momentum Conservation:

(1)

Where:

, - Initial and final momemtums of the small object, measured in kilogram-meters per second.

, - Initial and final momentums of the big object, measured in kilogram-meters per second.

If we know that , and , then the final momentum of the big object is:

The magnitude of the large object's momentum change is:

The magnitude of the large object's momentum change is 3 kilogram-meters per second.

car stops. he keeps going = he has inertia