How Do You Calculate Stress and Strain in a Stretched Copper Wire?

[DizzyDoo]

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

Homework Statement

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

Homework Equations

(Pie)r²
strain = extension/original length
stress = Force/area

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.

 

[PhanthomJay]

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

Homework Statement

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

Homework Equations

(Pie)r²
strain = extension/original length
stress = Force/area

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 you mean 7.8 x 10^-7 m^2[/color]
B) Extension/Original length= 0.85/2.3 = 0.37 Right equation, but again your units are lacking and decimal point is off[/color]
C) Hmm, they ask for stress but there is no force given, so how do I work that out? You have Young's modulus and you have calculated the strain...what is the formula that relates stess and strain?[/color]
d) Now they ask the force needed to cause the stress, but I need that to work out the stress. Very confusing once you have the stress, the force should be easy to calculate[/color]

Any help is greatly appreciated.

see above in red [/color].