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Homework Help: Solving for Simultaneity problem

  1. Aug 28, 2010 #1
    1. The problem statement, all variables and given/known data
    How fast must the observer be moving in the +x-axis direction so that events A and B occur simultaneously?

    2. Relevant equations
    I am currently in the solving stage of this problem and I need some help factoring this out/entering it into Octave. Can anyone help?


    3. The attempt at a solution
    I am currently nearing the end of the (*hopefully) working solution. I am currently here:

    1.296e33=v^2(9e16-v^2)

    How do I solve from here either by hand, or by entering it into MATLAB/Octave? I appreciate all help! Thank you very much for your time.
     
  2. jcsd
  3. Aug 29, 2010 #2

    vela

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    In relativity, it's generally better to solve for β=v/c rather than v alone. It just keeps things neater. In your case, if you divide by c4, you'll get

    [tex]\beta^2(1-\beta^2) = 0.16[/tex]

    This is a quadratic in β2. Solve for β2 by factoring, if possible, or by using the quadratic equation.
     
  4. Aug 29, 2010 #3
    Thank you for your reply. However, by entering that function into my calculator, I find that the function has 4 zeros. Even if I assume that the velocity cannot be negative (because we're moving in the +x direction), I still have two values that are directly proportional by a factor of 2. How do I determine which one it is? The values end up being 0.447214c and 0.89443c FYI. Thanks.
     
  5. Aug 29, 2010 #4

    vela

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    I can't say as I don't know how you got that equation. I'm guessing to get to that point you squared another equation, which introduced a spurious solution. If that's the case, you just have to try both solutions in the original equation and see which one works.
     
  6. Aug 29, 2010 #5
    I found the zeros to the equation you gave me above...
     
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