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Homework Help: Wire tension and extension

  1. Apr 22, 2010 #1
    1. The problem statement, all variables and given/known data

    A wire of diameter 5.0 mm supports a 2.8kg load.
    (a) Determine the tension in the wire
    (b) The original length of the wire was 2.0m Calculate its extension when supporting the load.



    2. Relevant equations

    Young's modulus for the material of the wire = 2.0 x 10^7N m^-2



    3. The attempt at a solution

    a) Tension - Weight = mass x acceleration
    acceleration is 0
    Therefore
    Tension = Weight
    W=mg=2.8 x 10
    =28N

    b) I have the equation E=(force(F)/area(A)) / (extension(ex)/original length(l))
    Can I:
    (F x ex) = (A x l)
    ex= (A x l)/F?

    Which would give ((2.5x10^-3)x2.0) / 28 = 0.18x10^-3m (2s.f.)

    Please let me know if my method is good?
    Thank you
     
  2. jcsd
  3. Apr 22, 2010 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes, good.
    Yes. since (F/A)/(ex/l) is Fl/A(ex) , you might want to rewrite it as E = Fl/A(ex)
    your algebra is off. Use the formula I gave you, multiply both sides by (ex), and then divide both sides by E , and see what you get for ex = ??? You should also check your units to see if you are getting (ex) in length units; if you are not, then your equation is wrong.
     
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