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Homework Help: Special Relativity - 2 observers - 2 frames of reference

  1. Sep 21, 2012 #1
    1. The problem statement, all variables and given/known data
    An observer in frame S standing at the origin observes two flashes of colored light separated spatially by Δx = 2300 m. A blue flash occurs first, followed by a red flash 5 µs later. An observer in S ' moving along the x axis at speed v relative to S also observes the flashes 5 µs apart and with a separation of 2300 m, but the red flash is observed first. Find the magnitude and direction of v.

    2. Relevant equations
    I believe the necessary equation is v = Δx/Δt

    3. The attempt at a solution
    So I initially thought I would simply have to plug in to the above equation Δx = 2300 m and Δt = 5 μs. But now I am realizing that would not give me the velocity of the observer.
    To find the velocity of the observer would I have to know the distance he traveled?
    And then use Δt = 5x10^-6?
  2. jcsd
  3. Sep 21, 2012 #2


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    Science Advisor

    You titled this "special relativity" but you haven't used any formulas from relativity.
  4. Sep 23, 2012 #3
    I figured I could use x = γ(x' + vt') {The lorentz equation for distance}
    And then since I am given the spatial separation Δx,
    Δx = γ(xo' + vt2' - γ(xo' + vt1'
    Then I could solve for v, but that still did not work
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