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Homework Help: Youngs Modulas

  1. May 22, 2005 #1
    Youngs Modulus

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

    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: May 22, 2005
  2. jcsd
  3. May 22, 2005 #2

    dextercioby

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    The cross sectional area is wrong...

    Daniel.
     
  4. May 22, 2005 #3
    mmm, wires, 3.142r^2...
     
  5. May 22, 2005 #4

    dextercioby

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    Yep,that's right.And the length L is wrong as well.

    Daniel.
     
  6. May 22, 2005 #5
    calculation mistake rather than conceptual mistakes..
     
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