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Homework Help: Damped Oscillator

  1. Feb 6, 2014 #1
    Hey guys I'm new to the forum and having a little trouble with this conceptual problem.

    1. A block of mass m is connected to a spring, the other end of which is fixed. There is also a viscous damping mechanism. The following observations have been made of this system:

    i) If the block is pushed horizontally with a force equal to mg, the static compression of the spring is equal to h

    ii) The viscous resistive force is equal to mg as the block moves with a speed u.

    a) Write the differential equation governing horizontal oscillations of the mass in terms of m, g, h and u.

    b) for the particular case of u = 3√gh, what is the angular frequency of the damped oscillations?

    2. Relevant equations:

    mx'' + λx' + kx = 0

    3. The attempt at a solution:

    F = mg = -kh (x = h)

    F = mg = -λu for x' = u

    At this point I'm somewhat lost and not sure what they're looking for. If the viscous force = mg at velocity u, how can you translate that into a differential equation that covers all velocities of the mass? Any help would be greatly appreciated
  2. jcsd
  3. Feb 7, 2014 #2
    Can you obtain express ##k## and ##\lambda## from the conditions given?
  4. Feb 7, 2014 #3
    Oh, you're saying to set k = -(mg)/h and lambda = -(mg)/u and plug that into the diffeq? I don't know why that never occurred to me, thanks a lot for the suggestion!
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