1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Question regarding Rutherford's atomic model

  1. Feb 24, 2013 #1
    1. The problem statement, all variables and given/known data

    I am basically wondering how they got to the assumption that the Ve = 2Vα. I've tried it a few times and I keep on getting that based off of their other assumptions, Ve should =0, even though I know that this cannot possibly be the case.
    2. Relevant equations

    Conservation of momentum: Mava = Mav'a + meve

    Conservation of energy: .5Mava2 = .5Mav'a2 + .5Meve2

    3. The attempt at a solution

    I really don't know what to do. I've tried starting under the assumption as given that Va≈Va', which leads to getting Ve=0. I tried to do a binomial expansion using the fact that Me<<Ma, but again I got zero. I'm really not sure how to approach this. Any help would be appreciated.
  2. jcsd
  3. Feb 24, 2013 #2


    User Avatar

    It's not an assumption, it's a conclusion.

    Set up the equations for an elastic collision in one dimension, then get a general solution for the final velocities of both particles. Don't put in any numbers or the like, just get a general solution. Then assume that [itex]m_1 >> m_2[/itex], and see what you get for [itex]v_{2f}[/itex].
  4. Feb 27, 2013 #3
    Thank you very much. That makes much more sense, I'm not really sure why I didn't just do that the first time. My mistake was not solving for Valpha' in terms of the other equations. Once I realized that I had to do that, it was much clearer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted