physics
posted by Jess .
at what altitude should a satellite be placed into circular orbit so that its orbital period is 48 hours? the mass of the earth is 5.976x10^24 kg and the radius of the eatrh is 6.378x10^6 m.

The velocity required to keep a satellite in a circular orbit derives from
Vc = sqrt(µ/r) where r = the radius of the orbit in feet and µ = the Earth's gravitational constant = 1.407974x10^16 yielding r = 57,064 miles. 
Ignore the previous response as it did not answer your question.
The required altitude to maintain a period of 48 hours derives from
T = 2(Pi)sqrt[r^3/µ] where T = the period in seconds, r = the orbital radius in feet and µ = the Earth's gravitational constant = 1.407974x10^16.
From this, r = 41,668 miles making the altitude 37,705 miles.
The velocity at this altitude is 8000 fps.