1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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

    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
    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
    or, tearth=t/γ
    equate the tearth
    Quadratic eq in v2*earth
    Last edited: Oct 14, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted