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What is the elastic modulus of the wire?

  • Thread starter joseg707
  • Start date
  • #1
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Homework Statement


A wire of diameter 0.2mm stretches by 0.20% when a 6.28-N force is applied. What is the elastic modulus of the wire?


Homework Equations


Elastic Modulus=F/A/L/[tex]\Delta[/tex]L


The Attempt at a Solution


r=.1mm=1x10-4m

6.28N/(2[tex]\pi[/tex]1x10-8/.02=5x109N/m2

The right answer is 1.0x1011.

What am I doing wrong?
 

Answers and Replies

  • #2
Doc Al
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Homework Equations


Elastic Modulus=F/A/L/[tex]\Delta[/tex]L
That should be (F/A)/(ΔL/L).
 
  • #3
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Oh, yeah. Well how do I calculate that? I know that the change is .2% if I use .002 or .2 as a value for [tex]\Delta[/tex]L/L I don't get the right answer. What is wrong with my calculation?
 
  • #4
Doc Al
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44,882
1,129
6.28N/(2[tex]\pi[/tex]1x10-8/.02=5x109N/m2
Area = pi*r². Looks like you have an extra factor of two in there. And ΔL/L = 0.002.
 
  • #5
32
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Ah! Thank you so much! I don't know why I was thinking are was 2*pi*r^2. Thanks a lot!
 

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