(a)[2]
Define the gravitational potential at a point.
(b)[1]
A stone with mass $m$ possesses gravitational potential energy $E_p$ at point X in a gravitational field. The magnitude of the gravitational potential at X is $\phi$. State the relationship between $m$, $E_p$ and $\phi$.
(c)[4]
An isolated spherical planet of radius $R$ can be treated as though all of its mass were concentrated at its centre. The gravitational potential at the planet’s surface is $-6.30 \times 10^7\,\text{J kg}^{-1}$. A stone of mass $1.30\,\text{kg}$ moves towards the planet so that its distance from the centre changes from $6R$ to $5R$. Calculate the change in gravitational potential energy of the stone.