Physics help?

Question

A satellite is in a circular orbit 6800 km above the Earth's surface; i.e., it moves on a circular path under the influence of nothing but the Earth's gravity. The acceleration of gravity is
g = 2.30051 m/s^2 at this altitude. The radius of the Earth is 6.37 x 10^6 m. The acceleration of gravity is 2.30051 m/s^2.
Determine the speed of the satellite. Answer in units of km/s.
Determine the time it takes to complete one orbit around the Earth. Answer in units of s.

Answer 1

The cetrifugal force on the satellite must equal the gravitaional force. The centrifugal force is given by m*(v^2)/R, where R is the distance of the satellite from the center of the earth. This R will be earth's radius plus the altitude. The gravitational force is m*g. equating these gives

v = √(R*g)

The circumference of the orbit is 2*π*R; the time it takes to complete one circumference (one orbit) is 2*π*R/v or

2*π*√(R/g)

Answer 2

Using circular motion ...
Centripetal force
F = (mv^2) / r and since F = ma..

ma = (mv^2) /r
a = (v^2) /r

then you can substitute your numbers to get speed (v)... i'm not going to state precisely what are the r and a supposed to be.