An Illinois State football player of mass m =72 kg runs at a speed of vi = 10 m/

Question

An Illinois State football player of mass m =72 kg runs at a speed of vi = 10 m/s toward our Panther defensive line. They collide head on head, and the running player is totally stopped.

1) With their helmets on, the players collide with each other through a time t =0.39 s. Find the magnitude of average force exerted on the player's head.

F=?

2) Suppose they were playing 100 years ago, when people didn't wear helmets. Their heads would have collided within t =0.019 s. Find the magnitude of the average force for this time. (Explain to yourself why the helmet is so important to the player.)

F= ?

Explanation / Answer

1.

The average force exerted on the player's head is,

Favg = dp/dt = m[v0 - v]/dt = 72 [10-0]/ 0.39 = 1846.15 N = 1.846e+3 N

2.

The average force exerted on the player's head is,

Favg = dp/dt = m[v0 - v]/dt = 72 [10-0]/ 0.019 = 37894.7 N = 3.79e+4 N

This force is very larger than the calculated value in part 1, so, the player must use helmet

to escape from risk.

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