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Rate of Increase problem. Please help

  1. Oct 18, 2009 #1
    1. The problem statement, all variables and given/known data

    When air expands adiabatically (without gaining or losing heat), its pressure P and volume V are related by the equation PV^(1.4)=C where C is a constant. Suppose that at a certain instant the volume is 450 cubic centimeters and the pressure is 81 kPa and is decreasing at a rate of 10 kPa/minute. At what rate in cubic centimeters per minute is the volume increasing at this instant?



    2. Relevant equations

    I have no idea what any relevant equations would be.


    3. The attempt at a solution

    I don't know really where to start but I figured the kPa would be 71 and then 61 and so on... Maybe I take the derivative of the entire thing but that's an option
     
  2. jcsd
  3. Oct 18, 2009 #2
    You have :

    PV^(1.4)=C

    Try differentiate it. If you do you will see it become a algebra problem where you will
    be solving for dv.
     
  4. Oct 19, 2009 #3
    I agree with tnutty, try differentiating it implicitly with respect to t(time).
     
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