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Special Relativity with 2 light beams moving towards each other

  1. Mar 16, 2014 #1
    1. The problem statement, all variables and given/known data

    If one light beam is heading toward you from the right, and another is heading toward you from the left, how quickly from the perspective of the right-moving beam is the left-moving beam approaching it?

    1) 0
    2) c
    3) 1.5c
    4) 2c

    2. Relevant equations

    (v+w) / (1 + cw/c2)

    3. The attempt at a solution

    I tried plugging in c into the equation for both v and w but it gives me (c + c) / (1 + c2/c2) which equals 2c. It is one of the possible answers but I know nothing can go faster than c so I'm thinking the answer is probably c. Am I right? If so, why? If not, what am I doing wrong?
  2. jcsd
  3. Mar 16, 2014 #2


    User Avatar
    Science Advisor
    Homework Helper

    (c+c)/(1+c^2/c^2) isn't equal to 2c.
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