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Homework Help: Mass hanging on spring

  1. Dec 8, 2005 #1
    A 6.00 kg mass suspended from a spring with spring constant, k = 975.0 N/m, extends it to a total length of 0.250 m. Find the total length of the spring when a 15.20 kg mass is suspended from it.
    I drew the free body diagram to get,
    ma= kx- mg.. since a= 0, kx=mg
    solving for x gave me mg/k
    So I did (6.00)(9.8)/ 975.0 = .0603 m
    Then I did (15.2)(9.8)/ 975.0 = .153 m
    I didn't really know where to go from here.. do I subtract the values? Or am I even going about this in the right way?
    Thanks
     
  2. jcsd
  3. Dec 8, 2005 #2

    Doc Al

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    Staff: Mentor

    Hint: Find the unstretched length of the spring.
     
  4. Dec 8, 2005 #3
    so to find the unstretched length I use Hooke's Law
    F= -kd
    So it would be like what I had before, mg/k= d
    (6.00)(9.8)/ 975 = .0603
    since the total length is .250, I do .250-.0603 to get .1990 m.
    Is this right?
     
  5. Dec 8, 2005 #4

    Doc Al

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    Staff: Mentor

    Right idea, but check the arithmetic.
     
  6. Dec 8, 2005 #5
    Ok I figured it out. Thanks Doc Al!
     
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