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 propotional to their distance from Earth and that speed is called: Recessional Speed. Recessional speed v of a galaxy a distancce r from Earth is given by v = H.r;
where H = 1.58e-18 (1/s) is called Hubble constant. There are 2 galaxies that have distances from Earth are: 5.00e22 (m) nd 2.00e25 (m). If the galaxies at each of these distances had traveled at their recessional speeds, how long ago would they have been at our location?

Explanation / Answer

Given hubbles constant H = 1.58*10^ -18 1 /s      recession speed of each galaxy                    v_ 1 = 5*10^ 22 * 1.58*10^ -18                            = 7.9*10^ 4   m /s                   v_2   =   2*10^ 25 * 1.58 *10^ -18 = 3.16*10^ 7 m/s                the relation between velocity , distance and time is                       ?V = ?x / time                     time    = ?X / ? V                               =   2*10^ 25 - 5*10^ 22   / ( 3.16*10^ 7 - 7.9*10^ 4 )                               = 6.3*10^ 18 s  

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