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

  1. Nov 8, 2009 #1
    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. jcsd
  3. Nov 8, 2009 #2
    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 = ?
     
  4. Nov 8, 2009 #3
    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=[tex]\sqrt{}4[/tex]=2
     
    Last edited: Nov 8, 2009
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