(a)[2]
Show that the gravitational field strength at the planet’s surface is $3.7\,\text{N kg}^{-1}$.
(b)[3]
A stone of mass $2.4\,\text{kg}$ is lifted from the planet’s surface through a vertical distance of $1800\,\text{m}$. Use the field strength from (a) to find the change in gravitational potential energy of the stone. Explain your working.
(c)
A rock, starting from rest at infinity, travels towards the planet. At point $P$, its height above the surface of the planet is $3.5D$, where $D$ is the diameter of the planet, as shown in Fig. 1.1.