1.At what depth $d$ below Earth's surface does acceleration due to gravity become equal to its value at height $h=R/2$?
2.A satellite of mass $m$ revolves in a circular orbit of radius $r$ around Earth of mass $M$. Find its binding energy and energy required to shift it to orbit of radius $2r$.
3.Calculate the gravitational potential and gravitational field at a distance $r$ inside and outside a uniform solid sphere of mass $M$ and radius $R$.
