Paper 2 Gravitational Fields Drills

Q1 Field and potential near a planet

A planet has mass $5.40\times 10^{24}\mathrm{kg}$ and radius $6.20\times 10^6\mathrm{m}$.

1. Calculate the gravitational field strength at the surface. [2]
2. Calculate the gravitational potential at the surface, taking zero at infinity. [2]
3. Explain why field strength is a vector but potential is a scalar. [2]

Q2 Superposition

Two equal spherical masses are fixed in space. Point P is halfway between their centres.

1. Explain why the gravitational field strength at P is zero. [2]
2. Explain why the gravitational potential at P is not zero. [2]
3. State how the answer would change if one mass were larger than the other. [2]

Q3 Circular orbit

A satellite moves in a circular orbit of radius $7.20\times 10^6\mathrm{m}$ from Earth’s centre. Take Earth’s mass as $5.97\times 10^{24}\mathrm{kg}$.

1. Show that the orbital speed is about $7.4\times 10^3\mathrm{m}{\mathrm{s}}^{-1}$. [3]
2. Calculate the orbital period. [2]
3. Explain why the satellite is accelerating even though its speed is constant. [2]