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Pistons, Heat, and Work

  1. Apr 24, 2006 #1
    A fas is in a cylinder is at pressure of 6000 Pa and a piston has an area of .1m^2. As heat is slowly added the piston is pushed up a distance of 5cm. Calculate the work done on the surroundings by the expanding gas. (Assume pressure stays constant).

    Thus far i found the force using
    P=f/a 6000Pa or 6000N/m^2=F/.1m^2 therefore F=600N Correct? i think i'm mixing up units, but then i used
    W=1/2F(s^2) > 1/2(600N)(5cm)^2 > i get 7500N/cm^2 but these units dont seem right for work?
    Can you help me with my units and this is the work done by the gas right?

    To find the internal energy if 52J of heat is added do i just use Q=IE+W?
  2. jcsd
  3. Apr 24, 2006 #2

    Andrew Mason

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    [tex]W = P\Delta V[/tex]

    You are trying to use W = force x distance but Fds = PAdS = PdV. It is much easier to use PdV.

    What is the change in volume? Multiply that by the pressure to get the work done. On a PV diagram, Work is the area under the graph.

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