Radius of synchronous satellite from a planet

[galuda]

[SOLVED] radius of synchronous satellite from a planet

Homework Statement

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.

Homework Equations

Kepler's 3rd law

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?

 

[D H]

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.

 

[galuda]

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

 

[galuda]

yes that worked thank you very much

 

[D H]

You're welcome.