Relativistic Velocity Addition

  • Thread starter Oijl
  • Start date
  • #1
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Homework Statement


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?


Homework Equations


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

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:

Answers and Replies

  • #2
114
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Nevermind, got it just after I posted. I needed a negative! Always a negative.
 

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