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!

Conservation of energy and momentum of a proton

  1. Feb 9, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider a head-on, elastic collision between massless photon (momentum Pnot and energy Enot) and a stationary free electron. Assuming that the photon bounces directly back with momentum p (in the direction of -Pnot) and energy E, use conservation of energy and momentum to find p.

    2. Relevant equations
    massless: E=pc
    Maybe relevant...but probably not : E=hf

    3. The attempt at a solution
    I'm assuming that p is the momentum of the electron, because it is the only momentum not denoted in the problem. Note: Pnot is momentum of photon before collision, p is momentum of photon after collision, and m is the mass of the electron. I've set up this:

    (Pnot)c + mc2 = pc + [tex]\gamma[/tex]mc2
    Pnot=pe - p

    I remove a c from the top equation and isolate Pnot on the left side.
    Pnot= p + [tex]\gamma[/tex]mc - mc

    I plug this into the second equation

    p + [tex]\gamma[/tex]mc - mc = pe - p = [tex]\gamma[/tex]mu - p

    From here I try a couple different things, but my main method seems to be putting p on one side and pulling things out

    2p= m([tex]\gamma[/tex]u - [tex]\gamma[/tex]c + c)

    thanks for any help
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted