Radius of synchronous satellite from a planet

1. Dec 2, 2007

galuda

[SOLVED] radius of synchronous satellite from a planet

1. The problem statement, all variables and given/known data
A "synchronous" satellite, which always remains above the same point on a planet's equator, is put in orbit about a planet similar to Jupiter. This planet rotates once every 7.8h, has a mass of 1.8e27kg and a radius of 6.99e7. Given that G = 6.67e-11 calculate how far above jupiter's surface the satellite must be.

2. Relevant equations
Kepler's 3rd law

3. The attempt at a solution
well I converted the 7.8 hours to seconds which was 28080 seconds, then did (28080^2*g*1.8e27)/4pi^2, then took the cube root of all that. However that's not right. Any ideas?

2. Dec 2, 2007

D H

Staff Emeritus
The expression you used yields the distance between the center the planet and the satellite. You were asked for the height of the satellite above the surface to the planet.

3. Dec 2, 2007

galuda

oh so I just need to subtract the planet's radius from my answer?

4. Dec 2, 2007

galuda

yes that worked thank you very much

5. Dec 2, 2007

D H

Staff Emeritus
You're welcome.