# Young's modulus

1. Aug 21, 2005

### WY

Hey

I need some help with this question - i got part A but not B
Bone, which has Young's modulus of 1.5x10^10 Pa can undergo only a 1.2% decrease in length before fracturing,
a) what is the maximum force that can be applied to a bone whose minimum cross-secitonal area is 3cm^2 without fracturing.
b) what is the maximum height from which a 70 kg person could jump without fracturing the tibia. Assume the stress is the same in both legs and that the time between first touching the floor and coming to rest is 0.035s

part a i got the answer of 4.5x10^6 N

for part b i know the man's weight will b 686 N and that I will double the amount of force since there are two bones instead of just the one - but I am now stuck as to what to do next! could someone point me in the right direction as what to do?

2. Aug 21, 2005

### Fermat

It's an impulse thing.

What speed will he hit the ground at?
What is the change in (his) momentum?
What is the impulse?
What is the Impulsive Force?
etc.