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## Homework Statement

A planet with a mass of 8.99·1021 kg is in a circular orbit around a star with a mass of 1.33·1030 kg. The planet has an orbital radius of 1.21·1010 m.

a) What is the linear orbital velocity of the planet?

b) What is the period of the planets orbit?

c) What is the total mechanical energy?

## Homework Equations

Keplers 3rd law

[itex] (T^2/R^3)=(4π^2/G M) [/itex]

## The Attempt at a Solution

I figured it would be easier to solve b first, So I solved for T

[itex] T=sqrt((4π^2*R^3)/(G M)) [/itex]

and came up with 6.2784...*10^5. But I am confused on what the units would be. Both seconds and years are wrong.