# Planetary Motion

#### myoplex11

1. The problem statement, all variables and given/known data
The sun rotates around the center of the milky way galaxy at a distance of about 30,000 light years (1ly= 9.5*10^15m). if it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume that the mass distribution of galaxy is concentrated mostly in a central uniform sphere.

2. Relevant equations

G Msun Mgalamy / r^2 = Mgalaxy v^2/ r

3. The attempt at a solution
r= (30000 * (9.5 * 10^5) ) m
v= 2 * pi * r / 200 million years
i know i have to convert the years into seconds is my setup right?

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#### mgb_phys

Homework Helper
You have the equations slighty wrong. Your's would cancel the mass of the galaxy leaving only the mass of the sun.

And yes - you should work in m/kg/s

#### myoplex11

i am not sure what equation to use

Homework Helper

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