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Homework Help: Hooke's law?

  1. Jul 23, 2011 #1
    1. The problem statement, all variables and given/known data

    A 50g mass hangs at the end of a hookean spring. When a 20g more is added to the spring, it stretches 7.0cm more. Find the spring constant.

    3. The attempt at a solution

    Isn't it just

    mg = kx

    mg/x = k

    Shouldn't m = 70g instead of 20g???

    My key says m = 20g?
  2. jcsd
  3. Jul 23, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    That would give the total elongation from the unweighted position, not the additional elongation.
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