# Homework Help: About Break fall

1. Dec 1, 2007

### jack1234

Question
A stuntman lands safely in an air bag to break his fall from the top of a 6-storey building. Explain how the air bag reduces the risk of the injury.

Attempts
The air bag provides a longer duration for the force of the ground to act on the stuntman, hence the impulse is lesser, and hence reduces the risk of the injury.

Is it correct? If no, what is the better answer?

2. Dec 1, 2007

### Dick

You are garbling the definitions of some of the words in your response. Whether the airbag is there or not the stuntman has to decelerate from his falling speed to zero. What causes injury is acceleration. Now rephrase your answer using what effect the duration has on magnitude of acceleration.

3. Dec 1, 2007

### jack1234

Thanks, this is another attempt:
Since F=(mv-mu)/t
Let u=the speed of the man and air bag when the air bag touch the floor
v=0
Hence F=-mu/t, according to Newton 3rd law, this is the magnitude of force that acted on the man.
Since the air bag provides longer duration for the u to change to 0, hence the larger t makes the F smaller, therefore reduce the injury of the man.

4. Dec 1, 2007

### Dick

From the phrasing of the question I think you can just explain yourself in words. I'm not sure the using formulas makes it any clearer.

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