# planetary motion

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• November 24th 2008, 04:54 PM
su-z-q
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?
please help me i'm sooo confused about these problem.(Headbang)
• November 24th 2008, 05:21 PM
skeeter
this is just a plug and chug into the formula problem ... where is your difficulty?
• November 25th 2008, 05:40 PM
su-z-q
Quote:

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!
• November 25th 2008, 05:43 PM
skeeter
Kepler's law of harmony ...

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