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I have to do an assignment, but I cannot go in for office hours to get help from my professor. Regretfully, I lost the sheet and forgot to grab another until just a few days ago and now I'm on my own. All I really need are the formulas.

Here goes:

1. I can do part a, but I am completely flabbergasted at part b.1. A 10-km-radius neutron star is spinning one-thousand times per second.

a) Calculate the speed of a point on its equator, and compare it with the speed of light.

b) Calculate the orbital speed of a particle in a circular orbit just above the neutron star's surface, and compare with your answer to part (a).

2. Calculate the total mass of the Galaxy lying within 20 kpc of the Galactic center if the rotational speed at that radius is 240 km/s.

3) Centaurus A lies at a distance of 4 Mpc from Earth. This galaxy has radiu jets that span across the sky -- from the end of one lobe to the end of the other lobe-- with an angular diameter equivalent of 28.5 full moon widths. If the jets are equal in length how long is one of them in pc. (hint: one full moon is .5 degrees in angular diameter)

4. According to Hubble's law, with Ho=70 km/sec/Mpc, how long will it take for the distance from the Milky Way Galaxy to the Coma Cluster to double? (Hint: You don't need to look up the distance to the coma cluster)

2. Need formula

3. Need formula

4. I believe I can do this one, but don't I need the velocity of the coma cluster to solve it?