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Special Relativity

  1. Jan 25, 2015 #1
    1. The problem statement, all variables and given/known data
    Alphonse decides to go for a joy ride in his Astro-Scooter. He maintains a speed of 0.604 c and is gone for 6.53 years according to his ship's clock. His twin brother Carl says he is full of beans. According to Carl, how long has Alphonse been gone?
    To=?
    T=6.53 years?
    v=0.604c
    c=3*10^8

    2. Relevant equations
    T= To/ (Sqrt of (1- v^2 / c^2)

    3. The attempt at a solution
    So first i noticed i had to convert the years into seconds because the other variables were in seconds (m/s). So i multiplied 6.53 by 365*24*60*60 to make it into seconds (205930080sec). Which then i plugged it into the formula as T. As for the velocity and the speed of light, the "c" cancels out because the velocity it measured by a fraction of the speed of light so then it would only look like this Sqrt of (1-0.604^2 ) for the denominator. I then multiplied the "T" by the denominator of "To" to get To by itself. The answer came out to be 164123044 seconds however i still got it wrong. Then i tried the other way where this time "T" was To , which came out to be 2583866150.5 seconds but still wrong, im not sure which variable is right and what i mis calculated. Help is appreciated thank you :)
     
  2. jcsd
  3. Jan 25, 2015 #2
    Look, ##\frac{v^2} { c^2}## is just a ratio. So you need not change the unit in this problem.
     
  4. Jan 25, 2015 #3
    My online assignment doesnt accept years as a unit though, only hours, minutes and seconds :/
     
  5. Jan 25, 2015 #4

    haruspex

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    Is that exactly what you entered? You seem to have an extra digit in there.
     
  6. Jan 25, 2015 #5
    No not exactly i had to put it in sig figs which was three, so it came out to be 2.58E9. Ignore the extra digit my bad X)
     
  7. Jan 25, 2015 #6
    I wouldn't have affect the answer anyways
     
  8. Jan 25, 2015 #7

    haruspex

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    It would, since what you first posted was 10 times too much.
     
  9. Jan 25, 2015 #8
    Oh, thought you were talking about the decimal place, my bad. Anyways got 258386615.5 , just tried entering it again, however still wrong :/ Thanks for the header though! :)
     
  10. Jan 25, 2015 #9
     
  11. Jan 26, 2015 #10

    haruspex

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    Then I'm stumped. 2.58E9 seconds looks right to me. Maybe... if you allow a year as 365.25 days, it just tips over to 2.59E9.
     
  12. Jan 26, 2015 #11
    Yeah still wrong dam i guess ill just ask my physics teacher about it this coming tuesday ill keep you posted hahaha thanks anyways though!! :)
     
  13. Jan 26, 2015 #12
    Turns out the online assignment didnt mention they took years, so my physics teacher forgot to mention he customized the answer to accept it in years as well. Problem solved thanks!!!
     
  14. Jan 26, 2015 #13

    haruspex

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    Thanks for letting me know.
     
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