Work Done in a polytropic process

Click For Summary
SUMMARY

The discussion centers on calculating the work done during a polytropic process for a gas in a cylinder-piston system, with initial conditions of pressure at 13,789.5 Pa and volume at 0.02832 m³, expanding to 0.08496 m³ with a polytropic index (n) of 1. The correct formula for work in this scenario is derived from the integral of pressure with respect to volume, specifically using the equation W = P1 * V1 * ln(V2/V1). The integration process is simplified due to the nature of the polytropic index being equal to 1, allowing for straightforward calculations.

PREREQUISITES
  • Understanding of polytropic processes in thermodynamics
  • Familiarity with integral calculus, specifically integration of functions
  • Knowledge of the ideal gas law and its applications
  • Ability to manipulate and rearrange equations involving pressure and volume
NEXT STEPS
  • Study the derivation of work done in polytropic processes using the equation W = ∫PdV
  • Learn about different values of the polytropic index (n) and their implications on work calculations
  • Explore the relationship between pressure, volume, and temperature in thermodynamic systems
  • Review examples of cylinder-piston systems in thermodynamics to solidify understanding
USEFUL FOR

Students and professionals in mechanical engineering, particularly those studying thermodynamics, as well as anyone involved in the analysis of gas behavior in cylinder-piston arrangements.

juggalomike
Messages
49
Reaction score
0

Homework Statement


A gas is trapped in a cylinder-piston arrangement. The initial pressure and volume are 13,789.5 Pa and 0.02832 m^3. Determine the work(kj) assuming that the volume is increased to 0.08496 m^3 in a polytropic process with n=1.


Homework Equations


m_1-2=∫PdV from 1 to 2


The Attempt at a Solution



I believe the equation for n=1 i would use is P1*V1*ln(V2/V1), however i have to show how i would get that from the intial integral, and i am completely lost as to how i can get there.

Also if this is not the correct forum for this post i am sorry, please let me know and i will
re-post it in the correct location.
 
Physics news on Phys.org
The ln term comes about because the integral of 1/x is ln(x).
Search wikibooks for polytropic process.
 
juggalomike said:

Homework Statement


A gas is trapped in a cylinder-piston arrangement. The initial pressure and volume are 13,789.5 Pa and 0.02832 m^3. Determine the work(kj) assuming that the volume is increased to 0.08496 m^3 in a polytropic process with n=1.


Homework Equations


m_1-2=∫PdV from 1 to 2


The Attempt at a Solution



I believe the equation for n=1 i would use is P1*V1*ln(V2/V1), however i have to show how i would get that from the intial integral, and i am completely lost as to how i can get there.

Also if this is not the correct forum for this post i am sorry, please let me know and i will
re-post it in the correct location.
Express P as a function of V and integrate. Since n=1 in PV^n = K, this is rather simple.

AM
 
Andrew Mason said:
Express P as a function of V and integrate. Since n=1 in PV^n = K, this is rather simple.

AM

Thanks a lot, knew it wasn't a hard question was just stuck on the sub part.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

Similar threads

Replies
49
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
6K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K
Replies
12
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K