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Find displacement of suspensions when after an earthquake you are given the freqetc

  1. Sep 29, 2008 #1
    1. The problem statement, all variables and given/known data
    4people with uniform mass= 72.4kg
    car mass= 1130kg
    earthquake strikes,car is stationary.
    vertical oscillations make car bonuce on suspensions.
    when frequency= 1.8 Hz car exhibits maximum Amplitude of vibration.
    Earthquake over,4 people leave the car quickly,what distance does the cars undamaged suspensions lift the car body as the people get out?



    2. Relevant equations
    sorry im new to this i dont understand what this section wants


    3. The attempt at a solution

    i took this as a forced oscillation and as a simple harmonic oscillation.
    total mass = 1419.6 kg
    Velcoity = 3.6*pi*Amax (Amax=max amplitude)
    this comes from Vel=omega*Amax
    omega=2*pi*Frequency

    Acceleration = 2Amax/period
    i dont know i thought this one up...
    as max displacement= Amax + A max
    and time taken => period = 1/frequency...

    Acc= 3.6 Amax

    x=displacement of car body by suspension...

    x=Asin(omega*t)
    x'=A*omega*sin(omega*t)
    x''= - omega^2 *(x)

    ...
    3,6Amax = -(2*pi*1.8)^2 *x

    => x= - 0.028*Amax

    my head is exploding someone please give me some hint...i have an awful feeling that this could be a lot easier....

    fiendishly difficult differential equations are suspected but I'm not sure how to relate everything...its kinda late here in Ireland!please have some pity...
     
  2. jcsd
  3. Sep 29, 2008 #2
    Re: Find displacement of suspensions when after an earthquake you are given the freq.

    I just thought that since they left the car quickly then t must be tending towards zero...?
    right track?
     
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