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Homework Help: What are the Stress and Strain in each rod?

  1. Nov 23, 2009 #1
    1. The problem statement, all variables and given/known data
    A copper rod of 2 meters is joined to a steel rod with length (ls) and with cross sectional area of 1.0cm2 and 2.0cm2 respectively the compound rod is subjected to an equal and opposite force of 3x104N.
    a) The length of the steel rod if the elongation of the steel rod is equal.
    b) What are the stress and strain in each rod?

    2. Relevant equations

    The modulus of copper : 1.0 x 10'' N/m2
    The modulus of steel : 2.0 x 10'' N/m2

    3. The attempt at a solution

    I just want to be honest guys.., I have not tried any solutions because I really don't know where to start. please help me
  2. jcsd
  3. Nov 23, 2009 #2


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi thetruth1988! Welcome to PF! :wink:
    (Do you mean "if the elongation of the steel rod and the copper rod are equal" ?)

    Hint: what is the elongation of the copper rod under an equal and opposite force of 3x104N ?

    Then what is the elongation of the steel rod under the same equal and opposite force, if the length of the steel rod is L ? :smile:
  4. Nov 23, 2009 #3
    F_steel = (E_steel A/L) ΔL_steel

    omg! sorry.., I really dont know what to do.. :'( can you help me out with an equation?
  5. Nov 23, 2009 #4
    This looks like a question were you should use Youngs Modulus. Look that up and use it; it should solve the problem...
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