Q 8.2      p.203

para1 = {ii ->  m l^2, ct ->  c l1^2,  
          kt ->  k l1^2  }   /. m ->  m1 + ms/3

eq1 = 
      ii θ''[t] + ct θ'[t] + kt θ[t] /. 
        para1

eq2 = Simplify[Expand[eq1/l^2 /. θ ->  x]]

para2 = {m1 -> 10, ms -> 3, l1 -> 1, l -> 2, 
        k ->  100000, c ->  200}

eq2 /. para2

{ωn, ζ} = 
      N[{Sqrt[25000 / 11] /2/Pi, 50/2/Sqrt[25000 11]}]

gs = 1/(25000  + 50 s + 11 s^2)

gt = InverseLaplaceTransform[gs, s, t]

Plot[gt 1000, {t, 0, 1.1}]

ga = gs ω^2 m1 ϵ /. 
              s ->  I ω /. ω ->  2 Pi f /. 
          para2 /. ϵ-> 1

Plot[Abs[ga], {f, 0, 10}, GridLines ->  Automatic]