Orbital velocity

Question

Your favorite GTA is orbiting Neptune at a height of 12500 km above Neptune's surface. Determine the speed of our illustrious GTA when orbiting Neptune.

Answer 1

Look up the radius of Neptune in meters. Call it R.

Look up the mass of Neptune in kg. Call it M.

h = height of circular orbit = 12,500,000 meters

G = constant of universal gravitation (look it up in Nm²/kg²)

Circular orbital speed is

v = √[GM / (R + h)]

Plug in the numbers and get v in meters/sec.