Question #109456

Explain how it is possible for a small child and a large football player to have the same momentum. If the small child and the large football player were running side-by-side (same velocity) which would take more force to stop? Why?

Expert's answer

What is momentum? It is mass times velocity. Therefore, at low velocity an adult footballer may have the same momentum as a not so heavy child running at a full speed:

On the other hand, momentum can be expressed as

The force that makes the footballer and the child stop is the force of friction. Assume that the coefficient of kinetic friction is the same for both:

Substitute this to the previous equation with force and expand the momentum:

Therefore, for the same speed it may theoretically take the same time for them to stop.

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