# Ratio of the velocities of two atoms, based on kinetic energy

1. Nov 8, 2009

### buttermellow

1. The problem statement, all variables and given/known data

An oxygen atom is four times as massive as a helium atom. In an experiment, a helium atom and an oxygen atom have the same kinetic energy. What is the ratio vHe /vO of their speeds?

2. Relevant equations
K=.5mv2

3. The attempt at a solution

.5mHe(vHe)2=.5(4mHe)(vO)2

I'm not sure what to do with that though, how to solve for the ratio.

2. Nov 8, 2009

### Fightfish

Have you learnt basic algebraic manipulation? You just have to rearrange the equation so as to get the ratio V(he)/V(o) on one side. eg. 5a = 3b, a/b = ?

3. Nov 8, 2009

### buttermellow

Oh my, I was making that much harder than it needed to be.

What I got:
.5mHe(vHe)2=2mHe(vO)2
mHe cancels to give (vHe)2=4(vO)2
(vHe)2/(vO)2=4
vHe/vO=$$\sqrt{}4$$=2

Last edited: Nov 8, 2009