Q.4
The acceleration due to gravity of a particle falling toward the earth
is $a = -gR^2/r^2$, where $r$ is the distance from the center of the earth
to the particle, $R$ is the radius of the earth, and $g$ is the acceleration
due to gravity at the surface of the earth. If $R = 3960$ mi, calculate
the escape velocity, that is, the minimum velocity with which a
particle must be projected vertically upward from the surface of the
earth if it is not to return to the earth. (Hint: $v = 0$ for $r = \infty$.)
