It has been found that, on average, galaxies are moving away from Earth at a spe

Question

It has been found that, on average, galaxies are moving away from Earth at a speed that is proportional to their distance from Earth. This discovery is known as Hubble's law, named for its discoverer, astrophysicist Sir Edwin Hubble. He found that the recessional speed of v of a galaxy a distance r from Earth is given by v = Hr where H = 1.58 10-18 s-1 is called the Hubble constant.
(a) What is the expected recessional speed of a galaxy 4.80 1022 m from Earth?
m/s

(b) What is the speed of a galaxy 1.60 1025 m from Earth?
m/s

(c) If the galaxies at each of these distances had traveled at their expected recessional speeds, how long ago would they have been at our location?
years ago

Explanation / Answer

a) , the galaxy's recessional velocity is v = Hr v= 1.58 * 10^-18 *4.8 *10^22 =7.584 * 10^4 b)similarly v= 1.58 * 10^-18 * 1.6 *10^25 =2.528 * 10^7 c) for Hubb's law t=1/H =1/1.58 * 10^-18 =6.33 * 10^17

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