# Homework Help: Young's Modulus Help

1. Aug 4, 2009

### greeto8

Had a problem with this question in my (Wilson Buffa Lou) College Physics book.

The problem says: A copper wire has a length of 5.0m and a diameter of 3mm. Under what load will its length increase by 0.3mm?
The answer in the back says 47N.

This is my work through the problem and I wanted to see where I went wrong.

delta L=0.3 x 10^-3m A=(3x10^-3)^2=A=(9x10^-6m^2) Lo=5.0m
Copper Wire=Y=11x10^10

ok....... So........Y=FLo/(delta)LA

F(5.0m)/(0.3x10^-3)(9x10^-6m^2)=(11x10^10)

F(5.0m)/(2.7x10^-9)=11x10^10

multiplying both sides by 2x10^-9

297N/m=F(5.0m) 297N/m/5.0m=59.4N My answer: 59.4N Any help greatly appreciated. Is my work getting close? Cant find enough examples for Young's Modulus, any direction in that matter is greatly appreciated too. Thank you for your time.
Ed

2. Aug 5, 2009

### method_man

A=(3x10^-3)^2=A=(9x10^-6m^2)

pi?
A=r2*pi
I just figured it out. In your formula you have to divide 3x10^-3 by 2 because you' re dealing with diameter.
I tried to solve it, and I get around 47 N

Last edited: Aug 5, 2009