A galaxy at a distance of 10 Mpc is moving away from us at a speed of 800 km/s.What would be the recession speed of a galaxy at a distance of 5 Mpc?

Question

Quizplus · Accepted Answer

According to Hubble's law, the recession velocity (v) of a galaxy is proportional to its distance (d) from us:
v = H0 x d
where H0 is the Hubble constant.

If the recession velocity (v1) of a galaxy at a distance (d1) of 10 Mpc is 800 km/s, then we can find the Hubble constant (H0) as follows:
800 km/s = H0 x 10 Mpc
H0 = 80 km/s/Mpc

Now, we can use this value of H0 to find the recession velocity (v2) of a galaxy at a distance (d2) of 5 Mpc:
v2 = H0 x d2
v2 = 80 km/s/Mpc x 5 Mpc
v2 = 400 km/s

Therefore, the recession speed of a galaxy at a distance of 5 Mpc would be 400 km/s. Hence, the answer is D.

A Galaxy at a Distance of 10 Mpc Is Moving