(a)[2]
Define gravitational potential at a point in a gravitational field.
(b)[1]
A stone of mass $m$ has gravitational potential energy $E_p$ at a point $X$ in a gravitational field. The size of the gravitational potential at $X$ is $\phi$. State the relation between $m$, $E_p$ and $\phi$.
(c)[4]
An isolated spherical planet of radius $R$ may be treated as if all of its mass is 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.