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How far does the piston move

  1. Jun 9, 2009 #1
    1. The problem statement, all variables and given/known data
    The figure shows a 50 kg lead cylindrical piston that floats on 0.68 mol of compressed air at 30°C. How far does the piston move if the temperature is increased to 300°C? (the base of the beaker is 10cm.

    A)130 cm B)1300 cm C)120 cm D)250 cm



    2. Relevant equations


    ?
    3. The attempt at a solution

    no clue
     
  2. jcsd
  3. Jun 9, 2009 #2
    Re: Pressure/pistons

    Think "Energy Balance"

    Can you relate the internal energy change due to [itex]\Delta T[/itex] to the work needed to raise the piston?
     
  4. Jun 9, 2009 #3
    Re: Pressure/pistons

    is this a proper equation U= W+Q?
     
  5. Jun 9, 2009 #4
    Re: Pressure/pistons

    Yes. That is the "Energy Balance" for a thermodynamic system.

    Now, what do each of the three terms represent?
     
  6. Jun 9, 2009 #5
    Re: Pressure/pistons

    internal energy= work + heat, and since temperature increases, internal energy increases also?
     
  7. Jun 9, 2009 #6
    Re: Pressure/pistons

    Yes. Internal energy in a direct measure of the temperature change, you should have read somewhere that:

    [itex]\Delta U=mc\Delta T[/itex] (or something similar depending whether it is a per mass basis or molecular basis) and that [itex]W=\int p\, dV[/itex]
     
  8. Jun 9, 2009 #7
    Re: Pressure/pistons

    ok so i have mass and change of T, how do i find C, also what do i do once i have change of U
     
  9. Jun 9, 2009 #8
    Re: Pressure/pistons

    Generally, values of specific heat are tabulated in your text.

    You tell me. What about your Work term? Your heat term Q is zero (I am assuming you can see why).

    What is the work here? Can you find distance the piston travels using the Work term?

    Hint: You were given area.
     
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