Q.What is a geostationary satellite? State its uses.

An Earth satellite -- natural (the Moon) or artificial -- is any object revolving around the Earth under the pull of gravity, which supplies exactly the centripetal force needed for its (approximately circular) orbital motion. Launching an artificial satellite requires a MINIMUM two-stage rocket: the first stage lifts it vertically to the desired height, and the second stage then imparts a precise HORIZONTAL velocity, since a purely vertical launch can only ever produce a fall-back or an escape, never a stable orbit. The specific horizontal speed needed, at a given height, for a stable circular orbit is called the critical (orbital) velocity, found by equating the required centripetal force to the available gravitational force: $v_c=\sqrt{\dfrac{GM}{R+h}}=\sqrt{g_h(R+h)}.$ …