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Homework Help: Lorentz Transformation of y-velocity

  1. Nov 7, 2012 #1
    1. The problem statement, all variables and given/known data

    A Particle moves with uniform speed V'y = Δy'/Δt' along the y'-axis of the rocket frame. Transform Δy' and Δt' to laboratory displacements Δx, Δy, and Δt using the Lorentz transformation equations. Show that the x-component and the y-component of the velocity of this particle in the laboratory frame are given by the expressions ... (under relevant equations)

    2. Relevant equations

    Vx = V rel
    Vy = Vy'(1-Vrel^2)^.5

    3. The attempt at a solution

    Okay so the text book i got this problem from is lacking in both directions and example problems. This is what I have so far..

    x = x' because the particle is moving along the y-axis

    Δt = vγy' + γt
    Δx = x'
    Δy= γy' + Vγt'
  2. jcsd
  3. Nov 7, 2012 #2
    or is it that
    t' = -Vrelγy+γt = γ(-Vrel(y)+t)
    y' = γy-Vrelγt = γ(y-Vrel(t))

    how should i continue?
  4. Nov 8, 2012 #3
    The relevant equations are not correct. If the particle is moving relative to the rocket, and the rocket is moving relative to the laboratory, then you have to use the relativistic Velocity Addition Theorem to get the velocity of the particle relative to the laboratory.
  5. Feb 6, 2014 #4
    I was able to get the given expressions by assuming that the rocket moves only along the x axis in the laboratory frame with relative speed v_rel, as suggested by v_x = v_rel, though the fault is on the book for not mentioning that specifically, thus forcing you to assume that the relative velocity could be in any direction.
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