What Is the Correct Calculation for Young's Modulus in This Problem?

AI Thread Summary
The discussion focuses on a calculation error regarding Young's Modulus for a brass wire. The user initially calculated Young's Modulus as 1.0 x 10^7, while the correct value is 1.3 x 10^11. Key mistakes identified include the incorrect calculation of the cross-sectional area and the initial length used in the formula. Participants confirm that the area should be calculated using the formula for the area of a circle, and the length should be accurately represented. The thread emphasizes the importance of precise calculations in determining material properties.
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Youngs Modulus

Hey guys, i tried this problem on youngs modulas and got the wrong answer

So i was wondering if anyone could tell me where i went wrong here or tell me how to do it properly.

Problem:

A 20cm brass wire of radius 1.0mm
experiences an elongation of 0.49mm
when a tensile force of 1.0 kN is applied.
Calculate the youngs modulas of brass.

E=σ/Є
σ = F/A
Є=ΔL/L

F=1000 N
A=0.2*0.001
ΔL=4.9*10^-4
L=1.0*^-3

Є = 4.9*10^-4/1.0X10^-3
σ = 1000/0.2*0.001
E= (1000/0.2*0.001)/(4.9*10^-4/1.0X10^-3)
That came out as 1.0*10^7 for me.
The answer is apparently 1.3*10^11

Any help on this would be good.
 
Last edited:
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The cross sectional area is wrong...

Daniel.
 
mmm, wires, 3.142r^2...
 
Yep,that's right.And the length L is wrong as well.

Daniel.
 
calculation mistake rather than conceptual mistakes..
 
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