# Homework Help: Relativity: Find the magnitude and direction

1. Oct 1, 2009

### endusto

1. The problem statement, all variables and given/known data
An observer in frame S standing at the origin observes two flashes of colored light separated spatially by Δx = 2400 m. A blue flash occurs first, followed by a red flash 5 μs later. An observer in S' moving along the x-axis at speed v relative to S also observes the flashes 5 μs apart and with a separation of 2400 m, but the red flash is observed first. Find the magnitude and direction of v.

2. Relevant equations
v = d/t
c = 3*10^8

3. The attempt at a solution
t2 = time until observer saw blue light
t1 = time until observer saw red light
c*t1 + c*t2 = 2400m = Δx (1)
t1 = t2 + 5μs (2)

substituting t1 with t2 + 5μs into (1):
c*(t2 + 5μs) + c*t2 = 2400m
c*(t2 + t2) = 2400m - 5μs*c
2*t2 = (2400m - 1498.96229m)/c
2*t2 = (901.03771m)/c
t2 = 901.03771m/c/2
t2 = 1.50276914 microseconds
t1 = t2 + 5μs
t1 = 6.50276914 microseconds

so basically all i found was the time it took the red and blue flash to reach the person. i don't know if i was supposed to do that. i don't really know what to do now so help is very much appreciated.