Solving a Physics Problem: Work Done by OR on a Gas

In summary: To do this, you need to use the integral notation. In this case, the integral is equivalent to the following:dW = dV pIn this case we have the initial and final values of V and p. So, W = (Vc - Vb) x 10-3m³ x (Pc - Pb) x 1.013 x 105Pa.
  • #1
kent davidge
933
56

Homework Statement



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Homework Equations



no

The Attempt at a Solution



no

Since the problem asks how much work was done by OR on the gas, I did not understand why the book's answer is 162 J instead ±81 J that I've found. (sorry my bad english)

Sorry, the correct question on the problem is how much work was done from b to c instead from a to b as it's in the image.
 
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  • #2
Show us how you got your answer, then we can point out what you did wrong. Also, be careful with your units. I don't know all the unit conversions but to use Joules the units for P and V are pascals and meters cubed, not atmospheres and liters.
 
  • #3
Okay.

dW = dV p

In this case we have the initial and final values of V and p. So, W = (Vc - Vb) x 10-3m³ x (Pc - Pb) x 1.013 x 105Pa, which gives W = 81.04 J.
 
  • #4
kent davidge said:
Okay.

dW = dV p

In this case we have the initial and final values of V and p. So, W = (Vc - Vb) x 10-3m³ x (Pc - Pb) x 1.013 x 105Pa, which gives W = 81.04 J.
You have calculated ##\Delta V\Delta p##. That is not the same as ##\int p.dV##.
 
  • #5
and how can I solve the integral for T?
 
  • #6
kent davidge said:
and how can I solve the integral for T?
In the graph, p is the y ordinate and V the x ordinate. So the integral is equivalent to ##\int y.dx##. what's a geometric interpretation of that integral?
 
  • #7
oh yes, I see that and I solve the problem by this way. But I wonder if there's anyway to solve this integral for T using only calculations without the graph. Is there a way?
 
  • #8
kent davidge said:
oh yes, I see that and I solve the problem by this way. But I wonder if there's anyway to solve this integral for T using only calculations without the graph. Is there a way?
Yes, but you first have to turn the graph into an equation relating p to V. Then plug that function into ##\int p.dV##.

Edit: When you say you solved the problem that way, are you referring to your solution in post #3? That solution was wrong.
 
  • #9
Ok. Thank you.
 
  • #10
kent davidge said:
Since the problem asks how much work was done by OR on the gas,

They do not want an answer with a ± sign in front of it. They want a positive number and they want you to determine whether it's "on" or "by".
 

Related to Solving a Physics Problem: Work Done by OR on a Gas

1. What is work done by a gas?

Work done by a gas is a measure of the energy transferred by the gas due to its change in volume or pressure. It is a form of mechanical work and is measured in joules (J).

2. How is work done by a gas calculated?

The work done by a gas can be calculated using the formula W = PΔV, where W is the work done, P is the pressure of the gas, and ΔV is the change in volume of the gas. Alternatively, it can also be calculated using the formula W = ∫PdV, where ∫ represents the integral sign and PdV represents the change in pressure and volume over a given process.

3. Can work be done on a gas?

Yes, work can be done on a gas. This occurs when external forces act on the gas, causing it to change in volume or pressure. In this case, the work done on the gas would be negative, as the gas is gaining energy from the external forces.

4. What are some examples of work done by or on a gas?

Examples of work done by a gas include a gas expanding against a piston, a gas compressing in a cylinder, or a gas being released from a pressurized container. Examples of work done on a gas include a gas being compressed by a piston, or a gas being pumped into a pressurized container.

5. How does work done by a gas relate to the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, but it can be transferred or converted from one form to another. The work done by or on a gas is a form of energy transfer, and it contributes to the change in internal energy of the gas, as stated by the first law of thermodynamics.

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