Galaxy a is moving away from us with a speed of 0.85c relative to the earth. galaxy b is moving away from us in the opposite direction with a relative speed of 0.55c. assume that the earth and the galaxies are inertial reference frames. how fast is galaxy a moving according to an observer in galaxy b?

The speed of the galaxy A moving according to an observer in galaxy B is 0.95c.

Explanation:

Given that,

Speed = 0.85c

Let is the velocity of galaxy A relative to galaxy B, is velocity of galaxy A relative to Earth and velocity of Earth relative to galaxy B.

Let’s assume that galaxy A is moving to the right,along the +x direction, so its velocity relative to earth is

Galaxy B is moving along the–x axis with a speed of 0.55c relative to earth, so its velocity is

Using velocity additional formula

We need to calculate the velocity of the galaxy A relative to galaxy B

Using formula of relative velocity

Hence, The speed of the galaxy A moving according to an observer in galaxy B is 0.95c.

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