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Homework Help: But Pressure is Funner

  1. Apr 21, 2008 #1
    1. The problem statement, all variables and given/known data
    An automobile tire is inflated with air originally at 10.0°C and normal atmospheric pressure. During the process, the air is compressed to 26.0% of its original volume and the temperature is increased to 32.0°C.
    (a) What is the tire pressure?


    2. Relevant equations

    p1V1/t1=p2v2/t2

    3. The attempt at a solution
    i know this is simple but im just not getting the right answer I keep using p1V1/t1=p2v2/t2 but wrong answers come out. i used 1 atm for normal atmospheric pressure
     
  2. jcsd
  3. Apr 21, 2008 #2

    mgb_phys

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    Remember that T must be in Kelvin since you are dividing by it.
     
  4. Apr 21, 2008 #3
    yes it is in kelvin...i got 419903.5 is that right?
     
  5. Apr 21, 2008 #4

    mgb_phys

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    First estimate the answer!
    Temperature hasn't changed much in absolute terms
    volume has gone down by a factor of 4 - so we want a pressure of around 4 atm.

    V1 = 1
    V2 = 0.26
    P1 = 1atm
    T1 = 283K
    P2 = ?
    T2 = 305K

    1/283 = 0.26 P /305
    So P = (305 /283) / 0.26 = 4.1 atm or around 420KPa

    ps. That's an impressive number of significant figures given the data!
     
  6. Apr 21, 2008 #5
    it asks for it in pa thats y
     
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