申論題

1. Two spaceships travel in a straight line directly away from Earth. The leading ship A emits a light signal that its crew measure to have wavelength 300 nm. The pursuing ship B, which is behind A and moving in the same direction, receives that signal at a wavelength of 600 nm (see figure). Ship B's speed relative to Earth is 0.200 c, where c is the speed of light.

(a) Using the Doppler shift between the two spaceships, determine the speed VAB of ship A relative to ship B (express your answer as a fraction of c). (5 points)