R1B1)  In the station frame, the firecracker explodes at  t = 15 sec and x = 1000 m.  In the train frame, the explosion occurs at t' = 15 sec and x' = x -Bt = 1000 - (55 m/s)(15 s) = 175 m.

R1S2)  The main problem they have is that they are not allowing for the time it takes the light to travel from the flags to their eyes.

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Albert Einstein (1879-1955)

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and science."