Walker, Halliday & Resnick — Relativity: Problem 3

3 In Fig. 37-9, observer S detects two flashes of light. A big flash occurs at $x_1 = 1200\text{ m}$ and, $5.00\text{ }\mu\text{s}$ later, a small flash occurs at $x_2 = 700\text{ m}$. As detected by observer $S'$, the two flashes occur at a single coordinate $x'$. (a) What is the speed parameter of $S'$, and (b) is $S'$ moving in the positive or negative direction of the $x$ axis? To $S'$, (c) which flash occurs first and (d) what is the time interval between the flashes?