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Special Relativity - Help Please!

  1. Oct 9, 2011 #1
    1. The problem statement, all variables and given/known data
    Two twins start their clocks at the same time, one of them travels for 7 years at a speed of 4/5c, reverses direction and returns at half the speed. The other twin remains stationary, what is the difference in their age?


    2. Relevant equations
    t = t_p γ


    3. The attempt at a solution

    I'm hung up on the thought... when he reverses direction he travels at half speed. Intuitively I think that it takes him 14 years to return at half speed... but is this necessarily the case? How can I prove that it is necessarily 14 years for him to return (considering Lorentz contraction) or find the actual time it would take him to return?
     
  2. jcsd
  3. Oct 9, 2011 #2

    vela

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    14 years as measured by whom? Same question for the initial 7 years.
     
  4. Oct 9, 2011 #3
    The 7 years is as measured by the traveling twin's frame. So my intuition wants to say that his return is 14 years in his frame. However I think that this may be flawed due to lorentz contraction of the distance being traveled.
     
  5. Oct 9, 2011 #4

    vela

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    Yes, you're right. It'll be longer than 14 years in that case. Not only is he going half the speed, he's having to travel a longer distance.
     
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