Please help with galactic distances?

Question

Assuming a constant speed of 15000 km s, by how many megaparsec would the separation between us and another galaxy change over 2 million years. Know i need Hubbles constant here, but struggling

Answer 1

946,080,000,000,000,000 km.

Answer 2

As we don't know the original separation between the galaxies I'm not sure what use Hubble's constant is. Ho only applies to galaxies that are not gravitationally bound together so I suggest that you multiply the speed by time and divide by the km/pc conversion, but watch your units

Answer 3

wait why wouldn't you need the hubble constant? There is the speed it is moving away and the expansion of the universe. Right?

Answer 4

Why do you need Hubble constant?  You are given the speed 15000 km per second.

(15000 km/s) x (60 s/min) x (60 min/hr) x (24 hr/day) x (365.25 day/yr) x 2000000 yr / ( 3.09 × 10^19 km / Mparsec) = answer

Answer 5

I wish I was smart enough to know what the h**l you're all talking about.

Answer 6

No, you don't need the Hubble Constant. You're told that a galaxy is receding at 15,000 km / s and are ask how much further away it will be in 2 million years, in Mps.

( 15, 000 km / s ) ( 2,000,000 years ) ( 31,557,000 s / year ) ( 1 Mps / 3 x 10²² meters ) ( 1000 meter / km ) = .03 Mps.