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I Work Problem

  1. Jan 28, 2017 #1
    "It takes 100J of work to stretch a spring 0.5m from its equilibrium position. How much work is needed to stretch it an additional 0.75m."
    Attempt: w = ⌠abF(x)dx
    work = F x D
    100J = F x 0.5m
    F = 200J

    0.75 + 0.5 = 1.25
    w = ⌠0.51.25 200dx
    w = 150 J

    The correct answer: w = 525 J

    what did I do wrong? Thanks!

    Nevermind, I found the exact problem online, so sorry!
  2. jcsd
  3. Jan 28, 2017 #2
    Work is not constant in spring.You cant use W=Fd.You should take an integral
    (Carefull for the signs when you take an integral).
    Another thing that Questions ask "The work done by our force".
  4. Jan 28, 2017 #3
    My problem was that I forgot hooke's law.
    F = kx
    I can apply it to the given information to find the target solution.
  5. Jan 28, 2017 #4
    Any ideas How ?
  6. Jan 28, 2017 #5
    w = ⌠.51.25 kx dx
    you can solve for k by plugging in known integral...
    100 = ⌠0.5kxdx

    you should get k = 800
  7. Jan 28, 2017 #6
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