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Homework Help: Please check my answer. Do I have the right one?

  1. Jul 6, 2011 #1
    The original question:
    2 steel rods and copper each of 20mm diameter together support a load of 20 kN. Find the stresses in the rod. Take E for steel and copper as 2.05 GN/m^2 and 1.10 GN/m^2.


    for steel
    l=(20kN)(2m)/(0.0003141x3)(2.05 GN/m^2)=0.021
    stress= lE/L=(0.021m)(2.05 GN/m^2)/2m=21525000

    and should i do the same for copper?

    Attached Files:

  2. jcsd
  3. Jul 9, 2011 #2


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    Science Advisor
    Homework Helper

    defdek: Your answer is currently incorrect. What you typed would be three steel rods, which is not what the question says. You omitted the other relevant equations.

    You must list the relevant equations yourself. The PF rules state we are not allowed to list relevant equations for you, nor tell you how to approach or solve your homework problem. We can only check your math, after you do all of the work to figure out how to approach the problem. Hint 1: Try an equilibrium equation.

    By the way, the correct unit symbol for GN/m^2 is called GPa. Only write GPa; do not write its derivation each time. See the international standard for writing units (ISO 31-0).
  4. Jul 11, 2011 #3
    I found it. thanks for the hint
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