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Homework Help: 2012 F=ma problem 21

  1. Jan 21, 2013 #1

    I'm just training for the 2013 F=ma exam, and I took some old exams. I tried to do the 2012 exam, and could not figure out problem 21. Can anyone help me, please?

    1. The problem statement, all variables and given/known data
    A spring system is set up as follows: a platform with weight 10 N is on top of two springs, each with a spring constant of 75 N/m. On top of the platform is a third spring with spring constant 75N/m. If a ball with weight of 5.0 N is fastened to the top of the third spring and then slowly lowered, by how much does the height of the spring system change?

    (A) 0.033 m
    (B) 0.067 m
    (C) 0.100 m (correct answer)
    (D) 0.133 m
    (E) 0.600 m

    2. Relevant equations


    3. The attempt at a solution
    The bottom springs act as one spring with K=150 N/m, thus will contract 0.033 m under the weight
    The top spring will compress 0.067 m under the weight
    so is it just addition...?
    Last edited: Jan 21, 2013
  2. jcsd
  3. Jan 21, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Yes, that's all there is to it. You are just combining the two compressions to get the total compression.
  4. Jan 21, 2013 #3
    Thanks Doc Al!
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