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Homework Help: Spring mass system problem

  1. Dec 11, 2012 #1
    1. The problem statement, all variables and given/known data
    A mass of 4 kg is stretches a spring by 1 m. An external force of cos (!t)
    N acts on the mass. Assume that the damping constant is nonzero and gravity is 10 ms^-2.
    Consider a spring mass system described by the following IVP.

    u''+yu'+u = cos(wt)
    u(0) = 0
    u'(0) = 0

    1) Find the amplitude of the spring mass system in terms of w and y.

    3. The attempt at a solution

    The solution says

    R2 = 1/((1-w2)2+w2y2)

    But how is that the solution, I can't find how to compute the amplitude in my textbook, it just says R2=A2+B2.
  2. jcsd
  3. Dec 12, 2012 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    It comes from the general solution to the differential equation.
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