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Integrating MaxwellBoltzmann speed distribution 
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#1
Dec610, 07:54 AM

P: 2

1. The problem statement, all variables and given/known data
Let P(v) represent the MaxwellBoltzmann speed distribution. Basically what it comes down to is that I have to find the definite integral (0,inf) of P(v)*v^2 and get v_{rms} from this. 2. Relevant equations We are given the definite integral from 0 to inf for the function (x^4)*exp(x^2), which is (3/8)*Sqrt(Pi). 3. The attempt at a solution I first move all the constants in front of the integral and then the integral simplifies to (v^4)*exp(mv^2/kT). However, I have no idea what to do with the constants stuck in the exponent. How would I continue from here? Thank you beforehand. 


#2
Dec610, 08:04 AM

P: 2,179

You have to make a substitution. Set:
x=v*sqrt(m/(kT)). (Except I think it's really x=v*sqrt(m/(2kT)) and you forgot the 2. E= 1/2 mv^2). 


#3
Dec610, 08:47 AM

P: 2

Thanks, that seems to be a working solution! Do you know what the answer should be? 3kT/m? For some reason I get Sqrt(9kT/2m).
EDIT: Forgot to replace dv with the corresponding operator for x, dx*[(m/2kT)^(1/2)]. Got it now! 


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