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Homework Help: Colliding Particles

  1. Jun 3, 2010 #1
    1. The problem statement, all variables and given/known data
    An alpha particle is a nucleus of Helium. It has twice the charge and four times the mass of the proton.
    A proton and an alpha particle headed directly toward each other, had each initial speed of 3.9×10^−3 c when they were far away.Here, as is customary when describing processes involving nuclear targets, the speed is expressed as a fraction of c, the speed of light.

    What is the distance of closest approach between the proton and the alpha particle?


    2. Relevant equations

    potential energy and electric potential energy.

    3. The attempt at a solution
    following is a simplified attempt at solution

    k(Q_p)(Q_a)/r=(.5(M_p)V^2)+(.5(M_a)V^2)
    and solved for r and got 1.7X10^-13 m
    but i keep getting it wrong could some 1 tell me where i am going wrong
    the answer is 1.3X10^-13m
     
    Last edited: Jun 3, 2010
  2. jcsd
  3. Jun 4, 2010 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    The problem is the frame of reference you are using.

    At the point of closest approach, are the two particles stopped in the lab frame? Why, or why not?

    AM
     
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