Suppose that the body travels a height h before it starts it journey downwards and let the radius of the Earth be R. We shall solve the problem using conservation of energy.At the instant when a body starts to move upwards, it total energy is the sum of its kinetic energy and its gravitational potential energy and is given by
. When the body reaches its highest point, its has no kinetic energy and its potential energy is given by
. So we have,
Now if the acceleration of at the surface due to gravity is g, then we have,
