In order for a satellite to be in geostationary orbit it must be at a distance from the earth that corresponds to one orbit per day. That distance is indeed about 6R. The satellite at 2.5R will not be in a geostationary orbit but instead will orbit a faster rate than the required rate to be geostationary.
The fundamental equation of orbital mechanics is
GM = w^2 r^3
where M is the mass of the earth, w is rotational velocity of the satellite, and r is the distance of the satellite above the center of the earth. Thus for any two satellites in earth orbit GM is a constant and you have:
w_1^2 r_1^3 = w_2^2 r_2^3
From this you can ascertain what happens to w with changing values of r.
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Last edited by ChipB; Sep 6th 2013 at 08:12 AM.
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