physics help?

Question

1.Calculate the velocity of a satellite moving in a stable circular orbit about the earth at a height of 3600km...
During an Apollo lunar landing mission, the command module continued to orbit the moon at an altitude of about 100km. How long did it take to go around the moon once?

Answer 1

In order for the satellite to stay in orbit
F(centripetal)=F(gravitational)
mV^2/R=kmM/R^2

V^2=kM/R

V=sqrt(k M/R)
where
k - Universal gravitational constant
M- Mass of the planet
R - Radius of the orbit

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