Thermodynamics problem - adiabatic process

Click For Summary

Homework Help Overview

The discussion revolves around a thermodynamics problem involving an adiabatic process in a diesel engine cylinder. The original poster presents a scenario with initial conditions of volume, temperature, and pressure, and seeks to determine the final temperature and volume after work is done on the gas.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants question the original poster's calculation of the final temperature and the use of the adiabatic process equations. There are discussions about the relationships between pressure, volume, and temperature in adiabatic processes, as well as the implications of using incorrect values.

Discussion Status

Participants are actively engaging with the problem, with some providing guidance on the correct equations to use for adiabatic processes. There is a mix of interpretations regarding the final temperature and volume, and the original poster expresses frustration with the feedback from the homework platform.

Contextual Notes

There is mention of specific values and units that may be causing confusion, such as the conversion between Celsius and Kelvin, and the implications of the volume being compressed. The original poster also references guidance from a homework platform that may not align with their calculations.

Twoism
Messages
17
Reaction score
0

Homework Statement


One cylinder in the diesel engine of a truck has an initial volume of 600 cm^3. Air is admitted to the cylinder at 35 C and a pressure of 1.0 atm. The piston rod then does 500 J of work to rapidly compress the air. What is the final temperature and volume?
I found the final temperature to be 1000C, but I can't find the final volume


Homework Equations


PV^y=PV^y
W=deltaE
deltaE=nCv(change in temp)
y=1.4
PV=nRT

The Attempt at a Solution


I don't know, honestly. It's maddening not to even know what to do or where to start.
Help?
Thank you.
 
Physics news on Phys.org
Show your work, please. How did you get 1000 °C for the final temperature?

What do you mean on PV^y=PV^y? that pV^y is equivalent to itself? If you use the correct equation for the adiabatic process together with the ideal gas law, you can find the relation between the temperature and volume.

ehild
 
I meant PV^y stays constant throughout the adiabatic process. I guess it should be P1V1^y=P2V2^y.
What do you mean by the "correct" equation for the adiabatic process?

Also, I know the final temperature is the correct answer, but what I did was:
W=nCv(deltaT)
n=PV/RT
n=(101325)(.0006)/8.31(308)
Cv for air=20.85 (it's in my physics book)
W=500J
500=nCv(Tf-308)
Tf= 1000 C
 
Hahahaha, WOW. I hate masteringphysics.
I just wiki'd Adiabatic process and found the simple equation
VT[tex]^{\alpha}[/tex]=Constant
Where [tex]\alpha[/tex]=5/2 for diatomic gases (like air).
I found V[tex]_{f}[/tex] to be 17.3, but that was wrong because my temperatures weren't accurate enough.
Guess what though? Masteringphysics TOLD me to use those values after I entered in more accurate values.
WTF.
 
The temperature is 1010 K, not C°. In what units did you get that 17.3 for the volume? The original volume was 0.0006 m3, and it was compressed, how can it be larger then?

Always write out the units!

ehild
 
Masteringphysics told me to use 1000C for furture calculations in the problem, hence why it I got it wrong... And 17.3 cm^3, so it's not larger.
 

Similar threads

Replies
49
Views
4K
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
5
Views
3K
  • · Replies 11 ·
Replies
11
Views
5K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K