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Homework Help: PV^n=constant (refresher)

  1. Sep 14, 2008 #1
    1. The problem statement, all variables and given/known data
    A closed system consisting of 2 lb of a gas undergoes a process in which pV^n=constant. For: p1=20 lb/in^2 , V1=10 ft^3 and p2=100lb/in^2 V2=2.9 ft^3

    (a)What is n ?

    (b)What is the specific volume at states 1 and 2 in ft^3/lb?

    (c)Sketch the process on pressure-volume coordinates


    For (a), I don't need to convert the units all to feet or all to inches right? i can just say p1V1^n=p2V2^n correct?

    (b) Is just a matter of find the mass m=Weight/g

    (c) Is confusing me? Is this just a graph? With p on the horizontal axis and V on the vertical?


    Thanks!!!
     
  2. jcsd
  3. Sep 14, 2008 #2
    Okay, I got (a).....the units cancel anyway.

    But for (b) I cannot tell if they are giving me 2lb as a mass or as a weight. It's a thermodynamics book, so I don't know what the convention is? they did not specify lbf (force) or lbm (mass)
     
  4. Sep 15, 2008 #3

    Andrew Mason

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    Correct.

    [tex]P_1V_1^n = 5P_1(.29V_1)^n[/tex]


    Correct

    You have to plot points in between the end points as well.

    AM
     
  5. Sep 15, 2008 #4

    Andrew Mason

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    Are the units of pressure Force/area or mass/area?

    AM
     
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