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: Relatavistic Collision

  1. Mar 21, 2012 #1
    1. The problem statement, all variables and given/known data

    A particle a traveling along the positive x axis of frame S with speed 0.5c decays into two identical particles, a--->b+b, both of which continue to travel on the x axis. (a) Given that ma=2.5mb, find the speed of either b particle in the rest frame of particle a. (b) By making the necessary transformation on the result of part (a), find the velocities of the two b particles in the original frame S.

    2. Relevant equations

    β=pc/E, p*p=-(mc)^2, E^2=(mc^2)^2 +(pc)2

    3. The attempt at a solution
    I think the initial momentum in the rest frame should look like pi'=γ^2*ma*c(0,0,0,1-(V^2/C^2))
    Which can then be re-written as pi'=(0,0,0,ma*c). Which seems to make sense considering it says that the four momentum of object a in a's rest frame has a value of 0 for the normal 3 momentum and that the fourth time value is m*c.
    I think you should then find the speed of a "b" particle in the rest frame of a, I would think by using the invarience of momentum. That is that pi*pi=pf*pf, which should allow you to solve for the speed of b in the rest frame of a. But I'm not sure If I am approaching the problem right and how to proceed from what I think I am doing right. Help would be appreciated as the book seems to offer one example that feels quite different.
    Last edited: Mar 21, 2012
  2. jcsd
  3. Mar 21, 2012 #2
    Still stuck; not sure if I am lacking in understanding some of the equations and properties of whats being described or if I am missing some small obvious step or fact that will allow for one to find the solution.
  4. Mar 22, 2012 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    What's the energy of one of the b particles in the rest frame of a?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook