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Homework Help: Help solve this ODE really stuck!

  1. May 24, 2013 #1
    I am trying to solve this ODE and am stuck on this step! It is a mass balance of a tank where the volume and concentration are changing by time

    Fin*Co - Fout*C1 = d(C1*V)/dt
    Fin*Co - Fout*C1 = d(C1)/dt * V + d(V)/dt * C1

    where V = A*h (area and height, where area is constant and height is changing with time)

    Fin*Co - Fout*C1 = d(C1)/dt * Ah + d(h)/dt * A * C1

    I understand you need to take the laplace somewhere...don't know where though!
    Any ideas on how I would go about simplifying this?

    Thank you!
  2. jcsd
  3. May 24, 2013 #2


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    Science Advisor

    You appear to have two unknown functions, C1 and V, but only one differential equation.
    You cannot solve a single equation for two unknowns.
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