# Integrating Maxwell-Boltzmann speed distribution

by zebala
Tags: boltzmann, integral, maxwell
 P: 2 1. The problem statement, all variables and given/known data Let P(v) represent the Maxwell-Boltzmann 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 vrms 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.
 P: 2,070 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).
 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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