A geo stationary satellite orbits around the earth in a circular orbit of radius $36000km$. Then the time period of a spy satellite orbiting a few Kilometers above the earth's surface $(R_{earth}=6400 Km)$ will be approximately

Question

\[(a)\;\frac{1}{2}\;hour \quad (b)\;2\;hour \quad (c)\;1\;hour \quad (d)\;4\;hour \]