# Homework Help: Urgent Cant Figure This Out

1. Oct 3, 2004

### Faiza

If you jump from a desk and land stiff-legged on a concrete floor,
the chance is good that you will break a leg. To see how this
happens, consider the average force stopping your body when you
drop from rest from a height of 1.00 m and stop in a much shorter
distance d. Your leg is likely to break where the cross-sectional area
of the bone (the tibia) is smallest. This is at a point just above the
ankle, where the cross-sectional area of the bone is about 1.60 cm^2.
A bone fractures when the compressive stress on it exceeds about
1.60*10^8 N/m^2. If you land on both legs, the maximum force your
ankles can safely exert on the rest of your body is then about……..

2 (1.60*10^8 N/m^2) (1.60*10^-4 m^2) = 5.12*10^4 N.

Calculate the minimum stopping distance d that does not result
in a broken leg if your mass is 60.0 kg. Don’t try it! Bend your knees!

2. Oct 3, 2004

### Faiza

?????????? :'( anyone know how to solve this problem?

3. Oct 3, 2004

### Faiza

there arnt any formulas to apply........:[

4. Oct 3, 2004

### Faiza

Helllllllllllllpppppppppppppppppppppp

5. Oct 3, 2004

### e(ho0n3

I think bumping is illegal, but who knows. I read through this and the phrase "...stop in a much shorter distance d" is confusing me. If you are falling, why would there be a stopping distance?

6. Oct 3, 2004

### vsage

The stopping distance is the distance your body traveled (very very small) while comnig to a rest. To faiza, think of the problem in terms of impulse: F*deltaS = impulse. A really large impulse is generated by a karate chop as opposed to a punch by a boxer because of the time it took for the force being applied to be removed (small in karate chop's case and large in the boxer's case). It's the impulse that hurts not the force.

Last edited by a moderator: Oct 3, 2004