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Thermodynamics, find the work done from the graph

  • Thread starter Alice7979
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  • #1
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Homework Statement


Using the data presented in the accompanying pressure-versus-volume graph, estimate the work done (including the algerbraic sign) when the system changes from A to B to C along the path shown.



Homework Equations


The work done is the area from change in position and time
Work= PV

The Attempt at a Solution


I counted 5X6 from the initial position to the next for both AB and BC
Given 1000 Pa and .002 m^3
Work = 1000 * .002 *60 = 1200 J

Do I have to include the whole area under the red lines starting from A to C?
 

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  • #3
348
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Homework Statement


Using the data presented in the accompanying pressure-versus-volume graph, estimate the work done (including the algerbraic sign) when the system changes from A to B to C along the path shown.



Homework Equations


The work done is the area from change in position and time
Work= PV

The Attempt at a Solution


I counted 5X6 from the initial position to the next for both AB and BC
Given 1000 Pa and .002 m^3
Work = 1000 * .002 *60 = 1200 J

Do I have to include the whole area under the red lines starting from A to C?
Write down your answer completely, consider the value of P at A and B, correctly. Neither at A nor at B it is 1000 Pa. Think carefully they need to be different.
 
  • #4
Delta2
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Homework Statement


...Do I have to include the whole area under the red lines starting from A to C?...
Draw a vertical (vertical to the volume axis) line at A and another vertical line at C. At point A the vertical line is just an extension to the red line at A.

You have to include all the area under the red lines which is between those two vertical lines.
 
  • #6
Delta2
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I think it will be useful to answer the following questions:

What's the pressure at point B?
What's the pressure at point C?

And how you will calculate the total work if you know correctly these two pressures?
 
  • #7
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I think it will be useful to answer the following questions:

What's the pressure at point B?
What's the pressure at point C?

And how you will calculate the total work if you know correctly these two pressures?
I am still lost but the graph shows 1000 Pa 10 blocks up starting from 0 so would the pressure per block be 100 Pa? Then change in pressure (final to initial) is 10000. And the volume per block is .002 so I multiplied it by 12 blocks and got .024. The work done would be P*V so 10000* 240. I If I'm wrong, am I even close to getting it?
 
  • #8
haruspex
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It sounds like it should be
Should be what?
is the correct answer 180 J
Not even close.
the graph shows 1000 Pa 10 blocks up starting from 0
Are we looking at the same graph?
It shows that each little square is 104Pa vertically and 2x10-3m3 horizontally. So what work does one little square represent?
 
  • #9
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I just noticed that, I got it now. Thanks
 

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