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Homework Help: Simple Temperature problem

  1. Nov 22, 2008 #1
    1. The problem statement, all variables and given/known data
    In an internal combustion engine, air at atmospheric pressure and a temperature of about 20 degrees C is compressed in the cylinder by a piston to (1/8) of its original volume (compression ratio 8.0).

    Estimate the temperature of the compressed air, assuming the pressure reaches 38 atm.

    2. Relevant equations
    pv = nRt
    [tex]\Delta[/tex]v = [tex]\beta[/tex]Vo[tex]\Delta[/tex]T

    [tex]\beta[/tex] = .0034 for air

    3. The attempt at a solution
    If i let p1 * v1 / T1 = p2 * v2 / T2
    i can make the associations and end up with T2 = T1 * 38 / 8
    however this result is incorrect.
    note that i used pv = nRt for this result, i'm not sure if the other equation should be used or not,
    i've only gotten garbage answers using it thus far.

    Any help would be much appreciated,
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 22, 2008 #2


    User Avatar

    Try using the other equation you have, though I know not what it is, and then, [tex] \Delta V = (1-\frac{1}{8}) V_0[/tex], from which it seems that the original volume is not here required.

    -the final temperature is the change in temperature plus the original temperature
    Last edited: Nov 22, 2008
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