# Sequence of events in special relativity [closed]

I am taking a general education course on special relativity, and get quite confused by problems asking about which event happens first according to different observers. Is there an effective way to do this?

Let's focus on the following problem:

A train is traveling at constant speed $u$. A, B and C stand inside the train where B is in the middle of A and C. B' is standing outside along the track. Inside the train, A, B and C send light pulse to each other simultaneously at the moment when B passes by B'. Describe the sequence of events (sending pulses, receiving pulses) according to B'.

I get quite confused. Can someone give a hint?

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 Are you familiar with spacetime diagrams? The sequence of events according to B' is as easy as sorting events by their time coordinates. – Muphrid Dec 14 '12 at 4:26 Hi Hui - this is a site for conceptual questions about physics, not general homework help. If you can edit your question to ask about the specific physics concept that is giving you trouble, I'll be happy to reopen it. See our FAQ and homework policy for more information. – David Zaslavsky♦ Dec 14 '12 at 4:33

## closed as too localized by David Zaslavsky♦Dec 14 '12 at 4:33

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