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Tension Question?

  1. Sep 6, 2008 #1
    Two steel wires P and Q have lengths l and 2l respectively and cross sectional areas A and A/2 respectively. Both wires obey Hooke's Law.

    What is the ratio (tension in P/tension in Q) when both wires are stretched to the same extension?
  2. jcsd
  3. Sep 7, 2008 #2


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    You must show an attempt at solving this before we can help you (forum rules).
  4. Sep 7, 2008 #3
    Yeah, I got it but it's not the right answer...
  5. Sep 7, 2008 #4


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    If you post your attempt, perhaps we could help you out.
  6. Sep 7, 2008 #5
    F/A divided by Difference in L/L


    Thus Fl/A(Difference in L)

    L is doubled

    Area is halved
    hence in Q it should be 4
    while in P it is 1

    But the answer says that it is 4:1
  7. Sep 7, 2008 #6


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    That's a good attempt, you're very close.

    Stress/Strain must be the same for both wires, since that is Young's Modulus for the material.

    As you said, (L/A) is a factor of 4 larger for Q.

    What must F be for wire Q, in order that the ratio
    F L/(A ΔL)
    be the same for both wires?
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