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## Homework Statement

Two newly discovered planets follow circular orbits around a star in a distant part of the galaxy. The orbital speeds of the planets are determined to be 41.7 km/s and 55.5 km/s. The slower planet's orbital period is 8.04 years.

**(a)**What is the mass of the star?

**(b)**What is the orbital period of the faster planet, in years?

## Homework Equations

M= r

^{2}T/G

T= 2[itex]\Pi[/itex]r

^{3/2}/[itex]GM

_{E}\sqrt{}[/itex]

## The Attempt at a Solution

I assume that the radius of the slower moving planet must be found first. Also, as for finding the period, does that same r need to be found, or is this going to be a very elaborate "plugging in the variables" type of equation?

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