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Homework Help: What is the value of the damping constant?

  1. Sep 1, 2008 #1

    A damped harmonic oscillator involves a block of mass 2.0kg and a spring with a stiffness 10 N/m. The damping force is proportioanla to the velocity of the oscillator. Initially it osicillates with an amplitude of 25cm. Due to the damping, the amplitude fallsto three-fourth of this initial value after 4 complete cycles..

    (a) What is the value of the damping constant?
    (b) How much energy has been "dissipated" during the 4 cycles?

    Here are my thoughts..

    Initial A=0.25m
    after 4 cycle it reduced to = 3/4 * 0.25 = 0.1875m

    w=sqrt [ k/m - (b/2m)sq]
    = sqrt [ 10/2 - (bsq)/16
    = sqrt [(80-bsq) / 16 ]

    i will be using

    x(t) = A exp (-b/2m)t sin (wt + teta) -----------> equation 1

    at t= 0 for the first cycle A= 0.25m

    1 cycle = 2pi, after 4 complete cycle. it will be at 8pi

    therefore putting the values A= 0.25, t=8pi, m=2kg and w= sqrt [(80-bsq) / 16 ]
    into equation 1

    0.1875= 0.25 exp (-b/4) 8pi sin (w8pi) * sqrt [(80-bsq) / 16 ]

    here i solve for b...to get answer the first answer

    am i on the right track?
  2. jcsd
  3. Sep 2, 2008 #2
    mistake...for first Amplitude to occur...t= pi/2

    what i have done so far...correct?...

    help? hint?..critics?
  4. Sep 2, 2008 #3
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