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Homework Help: Piston question to find temperature and pressure

  1. Jul 28, 2011 #1
    1. The problem statement, all variables and given/known data
    Air is contained in a vertical cylinder fitted with a frictionless piston and a set of stops. The cross sectional area of the piston is 0.05m^2. The air, which is initially at 0.21 MPa and 430 C, is cooled as result of heat transfer to the surroundings. Assuming that during the decrease in volume PV=constant find (a) the temperature of the air inside the cylinder when the piston reaches the stops and (b) the pressure inside the cylinder if cooling continues until the temperature is 70 C. Assume the air behaves as an ideal gas with constant specific heat with k=1.4
    The piston is 1.2m in length, stops are placed halfway of the piston, dividing the piston in two parts of 0.6m.

    The attempt at a solution
    Cant understand where to start
  2. jcsd
  3. Jul 29, 2011 #2


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    Hi Nightlord and welcome to PF. Please follow the rules of this forum and use the template when you seek help with homework. Show us the relevant equations and tell us what you tried and what you think about the problem. We just don't give answers away.
  4. Jul 31, 2011 #3

    Andrew Mason

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    There is a problem with this question. If PV=constant, then temperature would be constant (since we assume it is an ideal gas). So PV cannot be constant during a cooling process.

    Also, if you are supposed to actually answer a) we would have to know where the stops are.

    Please provide the entire question and show us what you have done.

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