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henryc09
Nov2-09, 01:30 PM
1. The problem statement, all variables and given/known data
The distribution of the speed v of molecules, mass m, in a gas in thermal equilibrium at temperature T is given by:

P(v)dv=Av2e-(0.5mv^2)/(kT)dv

where k is the boltzmann constant and A is the normalising constant. Determine A such that

\int between 0 and \infty P(v)dv=1


2. Relevant equations



3. The attempt at a solution
Obviously the main problem is I don't think it's very easy to directly integrate this equation and so I assume there is some trick for why between those values you can see a value for A where that last relationship will hold. Just a point in the right direction would be helpful, thanks.

Mark44
Nov2-09, 02:26 PM
Here's your integral, nicely formatted in LaTeX:
\int_0^{\infty} Av^2e^{-\frac{0.5mv^2}{kT}}dv

I don't think there is any trick -- integration by parts will probably do the job. I would split it up as u = v, dw = ve-(0.5mv2/kT)dw.

henryc09
Nov2-09, 03:39 PM
To make it simpler I'll say that m/kT is B.

But when you integrate ve^-Bv^2 the first time you get (-e^-Bv^2)/2B

But then for integration by parts you need to integrate this again which as far as I can see you can't do using the basic integration techniques I know.