Calculating vrms of Helium in Mixture of Gases

[sheri1987]

Homework Statement

A gas bottle contains a mixture of Helium and Oxygen molecules (O2 is diatomic). The root-mean-square velocity for the O2 molecules is 482 m/s. Find vrms for the Helium atoms.

Homework Equations

1/2mv^2=1/2mv^2

and solve for velocity of He, however, i am not sure what numbers to plug in for the mass.

The Attempt at a Solution

I filled everything in but the masses, I know that oxygen is diatomic, or O2, but what does that mean I put in for the mass? Do I need to use the mass numbers by looking at a periodic table?

 

[Astronuc]

m would be the molecular mass for a polyatomic molecule, or atomic mass for one of the noble gases, which are monatomic.

This might be a useful reference - http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kinthe.html