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: Relativistic Velocity Addition

  1. Feb 11, 2010 #1
    1. The problem statement, all variables and given/known data
    Nevermind, got it.

    Two spaceships approach the Earth from opposite directions. According to an observer on the Earth, ship A is moving at a speed of 0.753c and ship B at a speed of 0.851c. What is the speed of ship A as observed from ship B? Of ship B as observed from ship A?

    2. Relevant equations
    v = (v' + u) / (1+ (v'u)/(c^2))
    and so
    v' = (u - v) / ((vu)/(c^2) - 1)

    3. The attempt at a solution
    u is the speed of A as observed from Earth.
    v is the speed of B as observed from Earth.
    v', then, would be the speed of A or B as observed from the other ship.

    The values 0.753c and 0.851c plugged in, I get 0.2728c = v'.

    The speed of one ship as observed by the other ship should be greater than either of the ship's speeds as observed on earth. So where am I incorrect?
    Last edited: Feb 11, 2010
  2. jcsd
  3. Feb 11, 2010 #2
    Nevermind, got it just after I posted. I needed a negative! Always a negative.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook