Is This Calculation of Work Involving an Exponential Function Correct?

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Homework Help Overview

The discussion revolves around the calculation of work involving an exponential function, specifically using the equation W=∫0∞PdV where P is defined as P=e-v². Participants are exploring the integration of this function and the methods to evaluate the integral.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss substituting the expression for P into the work equation and the subsequent steps of differentiation and integration. There is mention of a common technique involving polar coordinates and the Gaussian integral, as well as questions about the implications of the limits of integration.

Discussion Status

Some participants have provided guidance on the approach to take with the integral, suggesting the use of polar coordinates and referencing the Gaussian integral. There is an exploration of whether the interval from ∞ to 0 can be considered negligible, indicating a productive direction in the discussion.

Contextual Notes

Participants are navigating the complexities of integrating an exponential function and are considering the implications of the limits of integration in their calculations. The discussion reflects a learning process around the Gaussian integral and its application to the problem at hand.

kabailey
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W=∫0PdV



P=e-v2



Do I simply substitue P in the original equation, differentiate, then integrate?

W=∫0e-v2dV

W=∫0(e-v2)/2v

So far is this correct?
 
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kabailey said:
W=∫0PdV
P=e-v2
Do I simply substitue P in the original equation, differentiate, then integrate?

W=∫0e-v2dV

W=∫0(e-v2)/2v

So far is this correct?

No, it isn't. That integral is usually worked by a trick of multiplying it by itself and changing it to polar coordinates. See
http://en.wikipedia.org/wiki/Gaussian_integral
There they do it from ##-\infty## to ##\infty##, but the same idea applies.
 
LCKurtz said:
No, it isn't. That integral is usually worked by a trick of multiplying it by itself and changing it to polar coordinates. See
http://en.wikipedia.org/wiki/Gaussian_integral
There they do it from ##-\infty## to ##\infty##, but the same idea applies.

I was not familiar with the Gaussian intergral. Well since it's only half the distance I would divide by 2 ∴

W=∫0e-v2dV

=(√∏)/2|0

so does that mean that the interval of ∞ to 0 is negligible?
 
kabailey said:
I was not familiar with the Gaussian intergral. Well since it's only half the distance I would divide by 2 ∴

W=∫0e-v2dV

=(√∏)/2|0

so does that mean that the interval of ∞ to 0 is negligible?

The integrand is an even function so, yes, you can just divide the full integral by 2. The integal from on ##[-\infty,0]## equals the integral over ##[0,\infty]##.
 
thank you for your help. my final answer is W=(√∏)/2
 
kabailey said:
thank you for your help. my final answer is W=(√∏)/2

That's correct.
 

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