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Stress and Strain - Materials

  1. Nov 28, 2007 #1
    The last question on my homework (always the hardest).

    1. The problem statement, all variables and given/known data
    A wire of diameter 1.0mm and length 2.3m is made of copper. Young modulus is 1.1 x 10^11. Find:
    a) The cross-section of the wire in m²
    b) The strain if the wire is stretched by 0.85mm
    c) The stress
    d) The force necessary to cause the stress

    2. Relevant equations
    (Pie)r²
    strain = extension/original length
    stress = Force/area

    3. The attempt at a solution
    Here is my attempt, I get stuck at C, but please check what I've done so far.

    A) if (pie)r² then stick that into the calculator, and I get 7.8 x 10 ^7
    B) Extension/Original length= 0.85/2.3 = 0.37
    c) Hmm, they ask for stress but there is no force given, so how do I work that out?
    d) Now they ask the force needed to cause the stress, but I need that to work out the stress. Very confusing

    Any help is greatly appreciated.
     
  2. jcsd
  3. Nov 28, 2007 #2

    PhanthomJay

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    see above in red .
     
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