Barron's 2nd Edition DT Q75

Barron's Book

75) This problem asks us to find the speed of light as perceived by an observer on Spaceship B. Some people might try to use inertial reference frames to try to find the relative speed. With regular relativity, this would work. But for this problem, doing this is a big mistake.

According to Albert Einstein's postulates of special relativity, light will always travel and be perceives at the same speed(c ≈ 3 * 10^8 m/s). This means that the speed of Spacecraft A and Spacecraft B is irrelevant. Whether they are at rest, traveling at 0.8c, or really any other speed, the speed of light will always be perceived at c ≈ 3 * 10^8 m/s.

Answer: D