Galaxy peculiar velocities are typically about 300 km/s.How far away do you have to look in order to see recessional velocities that are 10 times this peculiar velocity? Note that the Hubble constant has a value of 70 km/s/Mpc.
A) 12 Mpc
B) 25 Mly
C) 37 Mpc
D) 43 Mpc
E) 52 Mpc

Question

Quizplus · Accepted Answer

The recessional velocity is given by v = H0 * d, where H0 is the Hubble constant and d is the distance. We are given that the recessional velocity is 10 times the peculiar velocity, so v = 10 * 300 km/s = 3000 km/s. We are also given that H0 = 70 km/s/Mpc, so d = v / H0 = 3000 km/s / 70 km/s/Mpc = 43 Mpc.

Galaxy Peculiar Velocities Are Typically About 300 Km/s