Two galaxies on opposite ends of the universe are moving away from the Earth. Each has a velocity of 200,000 km/s relative to the Earth. How fast would an observer in one of those galaxies see the other galaxy moving away?
A.200,000 km/s
B. between 300,000 and 400,000 km/s
c. between 200,000 and 300,000 km/s
D. 400,000 km/s
The correct answer is D. 400,000 km/s.
This is because the velocity of a galaxy relative to the Earth is the sum of the individual velocities of the two galaxies. Therefore, an observer in one of the galaxies would see the other galaxy moving away with a velocity of 200,000 km/s (its own velocity) plus 200,000 km/s (the velocity of the other galaxy), giving a total velocity of 400,000 km/s.