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Homework Help: A question in special relativity

  1. Feb 1, 2009 #1


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    A particle of mass m moves in a center of mass frame of reference with a momentum p=2m. The center of mass moves with a speed v along the axis in the frame of reference of the laboratory. What's the angle of the particle in the frame of reference of the laboratory.

    What i think I have to do is to calculate the speed of the particle in the laboratory frame of reference, than it is just a simple trigonometric calculation. But I don't really know how to do this.
  2. jcsd
  3. Feb 2, 2009 #2


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    Hi mck! :smile:
    uhh? :confused: that's v. :wink:

    Hint: momentum is the x,y,z components of 4-momentum, which is a 4-vector which transforms exactly the same way as an (x y z t) 4-vector.

    So split p into pcosθ and psinθ, and transform them separately. :smile:
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