If i measure the recession velocities of 2 galaxies and galaxy a has a velocity twice that of galaxy b, how far away is b if a is 200 mpc away? (remember that v = h0 x d)

100Mpc

Explanation:

Hubble deduced that the farther the galaxy is, the more redshifted it is in its spectrum, and noted that all galaxies are "moving away from each other with a speed that increases with distance", and enunciated the now called Hubble–Lemaître Law.

This is mathematically expressed as:

(1)

Where:

is the approximate recession velocity of the galaxy

is the Hubble constant

is the distance

Now, we have two galaxies A and  B ande we know the following:

Galaxy A has a velocity twice that of galaxy B

(2)

Galaxy A is 200 Mpc away

 (3)

According to Hubble Law:

(4)

(5)

Substituting (2) in (5):

(6)

(7)

(8)

If  (9)

(10)

Substituting (8) in (11):

(11)

Finally: