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Homework Help: Frequency response of a spring mass damper system

  1. Mar 24, 2009 #1
    Consider a system with m = 100, c = 100 and k = 400. If y(t) = 3sin(1.5t), determine x(t) and ft(t).

    I don't have a picture handy but the equations for the system turn out like this.

    mx''+cx'+kx = cy' + ky

    Transfer function = x/y = cy' + ky / mx'' + cx' + kx

    then w/a laplace transform i get cs + k / ms^2 + cs + k

    i replace the s' w/ (j * omega) and eventually reach the dimensionless form of the equation which is

    X(s)/Y(s) = 1 + 2(zeta)(w/wn)j / (1-((w^2)/(wn^2))+ 2(zeta)(w/wn)j

    I'm kinda lost from here. I don't think i understand what they're actually asking me to find. Does he want the magnitude of x(t) and ft(t) or what?

    any kick in the right direction is appreciated
  2. jcsd
  3. Mar 24, 2009 #2
    The problem statement said, "determine x(t) and ft(t)." These are real functions of time, not functions of the complex variable, s. That's what they said they want you to find.
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