Thermodynamics problem - adiabatic process

In summary, the problem involves a diesel engine with an initial volume of 600 cm^3 and air at 35 C and 1.0 atm. The piston rod does 500 J of work to rapidly compress the air. The final temperature and volume are unknown. The correct equation for the adiabatic process is PV^y=PV^y, and using it with the ideal gas law, the relation between temperature and volume can be found. The final temperature is 1010 K and the final volume is 17.3 cm^3. However, the original volume was 0.0006 m^3, so the final volume cannot be larger. It is important to always include units in calculations.
  • #1
Twoism
17
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
  • #2
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
 
  • #3
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
 
  • #4
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.
 
  • #5
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
 
  • #6
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.
 

FAQ: Thermodynamics problem - adiabatic process

What is an adiabatic process in thermodynamics?

An adiabatic process in thermodynamics is a process in which there is no exchange of heat between a system and its surroundings. This means that the system is thermally isolated and all changes in its internal energy are due to work done on or by the system.

How is an adiabatic process different from an isothermal process?

An adiabatic process differs from an isothermal process in that in an adiabatic process, there is no heat transfer, while in an isothermal process, the temperature of the system remains constant. In an adiabatic process, the energy change is solely due to work, while in an isothermal process, the energy change is due to heat transfer.

What is the equation for an adiabatic process?

The equation for an adiabatic process is PVγ = constant, where P is the pressure, V is the volume, and γ is the specific heat ratio of the gas. This equation is known as the adiabatic equation of state and is derived from the first law of thermodynamics.

How do you calculate the change in internal energy in an adiabatic process?

In an adiabatic process, since there is no heat transfer, the change in internal energy is equal to the work done on or by the system. This can be calculated using the equation ΔU = W = PΔV, where ΔU is the change in internal energy, P is the pressure, and ΔV is the change in volume.

What are some real-world examples of adiabatic processes?

Some real-world examples of adiabatic processes include the compression or expansion of gases in a piston, the flow of air through a nozzle, and the compression of air in a bicycle pump. Atmospheric processes such as thunderstorms and tornadoes can also be considered adiabatic processes.

Back
Top