De Broglie wavelength of an atom

[Molar]

In my book it is says,
DeBroglie wavelength of a particle at temp T is, λ = h/√(2mKT) and
DeBroglie wavelength of He atom is, λ = h/√(3mKT)

Well, λ = h/ mv and mv²/2 = (3/2) KT and so , λ = h/√(3mKT)
How to prove the first one..??
and why they are different...??

 

[Dr. Courtney]

Try and follow the format for asking HW questions.

 

[Molar]

Sorry for that...being new I didn't get it ...
Here it is..

Homework Statement

Prove that , DeBroglie wavelength of a particle at temp T is, λ = h/√(2mKT) and
DeBroglie wavelength of He atom is, λ = h/√(3mKT)
h = Planck's constant ; K = Boltzmann constantRelevant equations

λ = h/p ,
p = mv ,
mv²/2 = 3/2 KT


The attempt at a solution

For helium atom we take
mv²/2 = 3/2 KT
so, v = √ (3KT/m)
∴ λ = h/√(3mKT) ...(proved)

My question is for the deBroglie wavelength of a particle should I take
mv²/2 = 1/2 KT and proceed like before...??