## Finding the mass of our Galaxy and the amount of stars in our Galaxy

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 from the center (1 light year=9.5x10^15 meters). If it takes about 200 million years to make one rotation, estimate the mass of our Galaxy. Assume that the mass distribution of our Galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the mass of our sun (2x10^30 kg), how many stars would there be in our Galaxy?

2. Relevant equations

3. The attempt at a solution

For the mass of the Galaxy I got an answer of 3.44425x10^41 kg and I got 1.72213x10^11 stars. I'm pretty sure this isn't right. HELP!?
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 Recognitions: Homework Help Science Advisor That looks about right to me. Why do you think it's wrong?

 Tags centripetal force, circular motion, gravitation, mass, sun

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