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Homework Help: Mixing involving diffy q

  1. Sep 4, 2006 #1
    fluid with 5mg/cm^3 of drug enters bloodsteam at 100cm^3/hr, drug is absorbed by body tissue or otherwise leaves the bloodstream at a rate proportional to the amount present with a rate constant of .4(hr)^-1.

    so assuming the drug is always uniformly distrbuted throughout the bloodstream, the differential equation for the amount of the drug that is present at time t is:

    What i have done is:
    let D(T)=amnt of drug absorbned by the body, at time t (hrs), in mg

    so i got dD/dt= rate in - rate out

    i have the rate in=100(5) mg/cm^3 or 500 mg/cm^3
    and rate out= D(t)/.4

    so my equation is dD/dt= 500-D/.4 then i can just you seperation of varibles...

    what do you all think :grumpy:
  2. jcsd
  3. Sep 5, 2006 #2


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    Science Advisor

    Yes, separation of variables will work. You might also note that that is a "linear differential equation with constant coefficients". Either method will work.
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