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Basic Special Relativity

  1. Oct 14, 2013 #1
    1. The problem statement, all variables and given/known data
    A star is 27c*y away from the rest reference of earth. A rocket reaches star A from earth and according to clocks on it 12 hours have passed. How fast is the rocket traveling in earth's reference frame?


    2. Relevant equations
    tpγ=t
    Lp/γ=L


    3. The attempt at a solution
    The problem is under the category of length contraction and time dilation so I assume these are the two equations I must use. However when trying to do the problem I only was given t and Lp, and yet there are three variables (tp, L, and v). Help ;-(
     
  2. jcsd
  3. Oct 14, 2013 #2
    Can you calculate what time has passed wrt IRearth?
    (I am assuming Earth is assumed to be an IR and the ship doesn't accelerate.)
     
  4. Oct 14, 2013 #3
    yes, no acceleration.
    I don't think I can calculate the time wrt IRearth..? I would need to know the velocity to do that so I knew the gamma factor correct?
     
  5. Oct 14, 2013 #4
    vearth=dearth/tearth
    tearth=dearth/vearth
    plug and chug.
     
  6. Oct 14, 2013 #5
    I don't know t_earth though? I only know it took 12 years from the spaceships frame..? oh... is Vearth 27c*y / 12 years...? i'm a noob X_X
     
  7. Oct 14, 2013 #6
    but that's not REALLY the speed earth see's it moving is it? Because earth couldn't see the rocket traveling faster than C could it?
     
  8. Oct 14, 2013 #7
    tearthγ=t
    or, tearth=t/γ
    equate the tearth
    Quadratic eq in v2*earth
    *editted
     
    Last edited: Oct 14, 2013
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