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Homework Help: Steel wire holding fish

  1. Dec 29, 2011 #1
    1. The problem statement, all variables and given/known data
    An angler hangs a 4.50-kg fish from a vertical steel wire and 5*10^-3 cm^2 in cross-section area. The upper end of the wire is securely fastened to a support.
    a) Calculate the amount the wire is stretched by the hanging fish.

    The angler now applies a force F to the fish, pulling it very slowly downward by 0.500 mm from its equilibrium position.

    b)Work done by gravity
    c) Work done by the force F
    d) Work done by the force the wire exerts on the fish
    e) Change in elastic potential energy

    2. Relevant equations
    Young's modulus = Tensile stress/tensile strain=F/A*l0/Δl
    Newton's laws (?)

    3. The attempt at a solution
    Young's modulus for steel is 20^10 = 4.5g/(5*10^-7)*1.5/Δl and solve for Δl

    Then the work done by gravity is 4.5g*0.500/10^3

    But it doesn't seem like there is enough information about the forces to answer c) and d)... I tried setting the force equal to the weight, but that didn't work.

    Help is appreciated. ~
  2. jcsd
  3. Dec 29, 2011 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Don't forget proper units and conversion factors. Force is in Newtons, not kg. What is the wire length and units?

    The applied force can be determined by the fact that the wire stretches another 0.5mm when it is applied.
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