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Homework Help: Frequency of oscillation (in Hz) question help! Thanks

  1. Jan 10, 2012 #1
    1. The problem statement, all variables and given/known data

    A 320 kg wooden raft floats on a lake in equilibrium. When a 75 kg man steps carefully onto the raft, it floats 3.5 cm deeper into the water. When he steps off, the raft oscillates for a while.

    I figured out that the force constant is 21,000 Nm - first off, is that correct?

    Now my QUESTION is, calculate the Frequency of oscillation (in Hz) after the man steps off the raft??????

    2. Relevant equations

    3. The attempt at a solution

    I came up with...

    2pi sqrt (m/k)

    2pi sqrt (320/21,000) = .776 Hrtz
  2. jcsd
  3. Jan 10, 2012 #2


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    I see you used the spring equation F = kx and found the k (agree with 21000).
    I have some reservations about treating this situation like a spring, but it makes considerable sense and I can't think of an alternative. Anyway, continuing with the spring model, you would use
    T = 2pi sqrt (m/k)
    to find the period and then the frequency.
  4. Jan 10, 2012 #3

    Simon Bridge

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    Your reasoning is more important than your results.

    Treated like a mass on a spring?
    (75x9.8)N was enough for 3.5cm extension is 21000Nm - well done.
    You plugged that into the equation for period of a mass on a spring :(

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