X - Solving for Load in Young's Modulus Problem

AI Thread Summary
The discussion revolves around a physics problem involving a copper wire where the goal is to determine the load that causes a specific elongation. The original poster calculated the load to be 59.4N, but the answer in the textbook is 47N. After reviewing the calculations, it was identified that the diameter should be halved to find the radius when calculating the cross-sectional area. Correcting this error leads to the proper application of Young's modulus, resulting in the expected answer of approximately 47N. The conversation highlights the importance of using the correct dimensions in formulas related to material properties.
greeto8
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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
 
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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
 
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