# Stress and Strain - Materials

1. Nov 28, 2007

### DizzyDoo

The last question on my homework (always the hardest).

1. The problem statement, all variables and given/known data
A wire of diameter 1.0mm and length 2.3m is made of copper. Young modulus is 1.1 x 10^11. Find:
a) The cross-section of the wire in m²
b) The strain if the wire is stretched by 0.85mm
c) The stress
d) The force necessary to cause the stress

2. Relevant equations
(Pie)r²
strain = extension/original length
stress = Force/area

3. The attempt at a solution
Here is my attempt, I get stuck at C, but please check what I've done so far.

A) if (pie)r² then stick that into the calculator, and I get 7.8 x 10 ^7
B) Extension/Original length= 0.85/2.3 = 0.37
c) Hmm, they ask for stress but there is no force given, so how do I work that out?
d) Now they ask the force needed to cause the stress, but I need that to work out the stress. Very confusing

Any help is greatly appreciated.

2. Nov 28, 2007

### PhanthomJay

see above in red .