*Answer:* Let be the Earth's radius. The distance of the rocket from the
centre of the Earth is
. We know that the free-fall
acceleration of the rocket when its distance from the Earth's centre is (*i.e.*, when it
is at the Earth's surface)
is
. Moreover, we know that gravity is an inverse-square law (*i.e.*,
).
Hence, the rocket's acceleration is

Richard Fitzpatrick 2006-02-02