SAT Subject Physics Practice Question 148: Answer and Explanation
11. Two spaceships are traveling directly toward each other, one traveling at a speed of and the other at a speed of , as measured by observers on a nearby planet. The faster ship emits a radar pulse directed toward the approaching ship. What is the speed of this radar pulse, as measured by observers on the planet?
Correct Answer: C
Radar waves are electromagnetic waves, and the speed of all electromagnetic waves through empty space is measured by all observers to always be c (Postulate 2 of the theory of special relativity).