Consider three galaxies,Alpha,Beta and Gamma.An astronomer in Beta sees each of the other two galaxies moving away from him in opposite directions at 0.70c.At what speed would an observer in Alpha see the galaxy Gamma moving?
A)0.70c
B)1.4c
C)0.82c
D)0.94c
E)0.98c

Question

Quizplus · Accepted Answer

According to the principle of relativity, both Beta and Alpha observers should see the same relative velocity between Gamma and Beta, but in opposite directions. Therefore, the velocity of Gamma with respect to Alpha would be the vector sum of the velocities of Gamma with respect to Beta and Beta with respect to Alpha. Using the relativistic velocity addition formula, we get:
v = (0.70c + (-0.70c)) / (1 - 0.70c x (-0.70c) / c^2) = 0.94c
So the correct answer is D) 0.94c.

Consider Three Galaxies,Alpha,Beta and Gamma