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Homework Help: Mass-Spring Oscillation question

  1. Sep 18, 2006 #1
    I tried to work out this problem a few different ways but I never get the right answer.

    A block hangs in equilibrium from a vertical spring. When a second identical block is added, the original block sags by 8.00 cm

    What is the oscillation frequency of the two-block system?

    What I've done so far:

    Attempt 1:

    (Fnet)y=-ky
    2mg=-ky
    m=((-ky)/(2g))

    Then using T=2pi times sqaure root[m/k]

    puting in my m as what I found in terms of k, y, and g. The K's cancel and I am left with things I know and then calculate to find my T it turns out to be 0.40 seconds

    and then I finish off my problem with freqency= 1/period and get 2.5 Hz

    But this is incorrect.

    I probably made a wrong assumption but I can't put my finger on it. I hope someone can put me on the right track.

    Thank you.
     
  2. jcsd
  3. Sep 18, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What you want to do is find the spring constant in terms of m, y, & g. Assuming that y is the additional displacement from equilibrium, then:
    mg = ky (since one block is added)

    What mass goes here? (The system has two blocks now.)
     
  4. Sep 18, 2006 #3
    Thank you! That worked perfectly. I understand where I made my mistake now too.
     
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