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Homework Help: Pressure vs. Volume graph help!

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data

    Look at the PV diagram of a system above. The units for P and V are atmospheric pressure atm and liter L. Process A to B and B to C are straight lines on it.
    How much is the work done by the system from A to C in J?

    https://tycho-s.physics.wisc.edu/cgi/courses/shell/common/showme.pl?courses/phys103/fall08/homework/12/pv/pv.gif [Broken]

    HELP: In general, the work done in an expansion from some initial state to some final state is the area under the curve on a PV diagram. So determine the area under the ABC-curve.

    HELP: Each square on the diagram has an area of: 1.5 atm * 1 L = 1.5 atm L = 152 J. Estimate the numbers of squares below the ABC-curve and multiply that number by 152 J. Good luck

    3. The attempt at a solution


    Wab= pressure x change in volume= 303975 Pa(.004meters cubed)= 1215.9
    Wbc= pressure x change in volume= 607950 Pa(.006 meters cubed)= 3647.7

    W= Wab +Wbc

    but this is not correct. Can anyone help me?
     
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 23, 2008 #2
    I did what you said, i.e. counted the squares under the curve and multiplied that number by 152, but I do not get the same answer as you. Try dividing the area into two rectangles and two triangles and calculate those four areas separately. Use the formula for the area of a triangle rather than guessing how many squares make up the triangle. Hope that helps.
     
  4. Nov 24, 2008 #3
    thanks! that worked.

    I got the Area of the triangles to be 4 and 3 and the area of the rectangles to be 8 and 18. multiplied by 152 and got an answer of 5020 J.

    thanks for your help!
     
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