# Math Help - planetary motion

1. ## planetary motion

A planet orbits a star with mass 4.35e+30 kg. The semimajor axis of the planet's orbit is 2.94×1012 m. What is the period of the planet's orbit in seconds?
An extrasolar planet has a small moon, which orbits the planet in 336 hours. The semimajor axis of the moon's orbit is 2.22e+9 m. What is the mass of the planet?

2. this is just a plug and chug into the formula problem ... where is your difficulty?

3. Originally Posted by skeeter
this is just a plug and chug into the formula problem ... where is your difficulty?
which formula? i got a whole bunch!

4. Kepler's law of harmony ...

$T^2 = \frac{4\pi^2}{GM} R^3$