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V=? for Relativistic Mass,length contraction & time dilation

  1. Dec 6, 2016 #1
    1. The problem statement, all variables and given/known data
    Velocity Equations for Relativistic Mass,length contraction and time dilation.
    I was able to figure out one. This is not for homework. I want to learn these equations for future reference.

    2. Relevant equations
    upload_2016-12-6_19-41-12.png
    upload_2016-12-6_19-45-34.png

    upload_2016-12-6_19-56-3.png
    3. The attempt at a solution

    Length Contraction : v = c √{1-(l'/lo)^2}
    Time Dilation: ?
    Mass: ?
     
  2. jcsd
  3. Dec 6, 2016 #2

    Simon Bridge

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    Just so I understand how you are thinking so I can answer properly:
    How did you work out the length-contraction equation? Why not do the same thing for time dilation?

    Note: no such thing as "relativistic mass". Used to be a thing but it turns out not to be much of a useful concept.
     
  4. Dec 6, 2016 #3
    l'/lo = √{1-v^2/c^2}
    (l'/lo)^2 = 1-v^2/c^2
    1-(l'/lo)^2 = v^2/c^2
    √{1-(l'/lo)^2} = v/c
    c√{1-(l'/lo)^2} = v

    Mass increase has not been discontinued in my program.
     
    Last edited: Dec 6, 2016
  5. Dec 7, 2016 #4

    Simon Bridge

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    Why not do the same thing for time dilation?

    OK you need to do relativistic mass for passing exams - just understand that it is an out of date concept.
     
  6. Dec 7, 2016 #5
    1481091214815-575886308.jpg
    I just copied the equations from wiki to this platform but i now have come to realize they are the same.
    This is pretty self explanatory. i was given equations from my lessons that were essentially the same but all look different so i got confused. I didnt even look at the wiki equations closely until now :sorry:o_O:frown:
     
    Last edited: Dec 7, 2016
  7. Dec 7, 2016 #6

    Orodruin

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    Better still: Point your teachers to my Insight post What is relativistic mass and why it is not used much? or refer them to me. It is simply a concept that is not used in physics today and it is really just confusing people to use it. Unfortunately, the concept permeates much of the introductory physics literature - which often is not written by people with specialist knowledge on relativity - and therefore becomes used by teachers at pre-university and introductory university level.
     
  8. Dec 7, 2016 #7

    Simon Bridge

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    Well done.
    The form of the equations is ##x = \frac{y}{\sqrt{1-z^2}}## and you want to solve for ##z##.
    It does not matter what the actual letters are.

    It is more important to understand how to use the equations - that is the hard part to get your head around.
     
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