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An armada of spaceships that is 1.00 ly long (in its rest frame) moves with speed .800c relative to a ground station in frame S. A messenger travels from the rear of the armada to the front with a speed of .950c relative to S. How long does the trip take as measured in:

(a) the messenger's rest frame?

(b) the armada's rest frame?

(c) an observer's point of view in frame S?

I am having a very hard time with relativity right now... Do I use the relativistic velocity equation?

[tex]u = \frac {u^{\prime} + v}{1+u^{\prime} v/c^2} \mbox { (relativistic velocity)}[/tex]

Or any other equations like:

[tex]\triangle t = \gamma \triangle t_0[/tex]

[tex]L = \frac {L_0}{\gamma}[/tex]

The thing that would help me most and I would be most grateful for is if someone would answer one of the questions in detail offering reasoning for each step of the problem, and offer some hints on solving the other ones. Answers to compare with might be helpful too.

Thanks in advance.

-Mark

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# Homework Help: Relativity rest frame Question

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