CAIE A-Level Physics 13.4.3 Gravitational Potential Energy

Practise relating gravitational potential to potential energy, calculating EP = -GMm/r and applying energy conservation to work, transfer and motion.

Exam points

explain how gravitational potential leads to gravitational potential energy for two point masses
calculate gravitational potential energy using EP = −GMm/r and interpret its sign
relate changes in gravitational potential energy to work, energy transfer or movement in a gravitational field

[Maximum number: 3]

The sphere in (b) is a planet with radius r of $6.4 \times 10^{6} \mathrm{~m}$ and mass M of $6.0 \times 10^{24} \mathrm{~kg}$ . The planet has no atmosphere.

A rock of mass $3.4 \times 10^{3} \mathrm{~kg}$ moves directly towards the planet. Its distance from the centre of the planet changes from 4 r to 3 r.

Calculate the change in gravitational potential energy of the rock.
change =

gravitational potential energy = (-) GMm / R

C1

change $=\left(6.67 \times 10^{-11} \times 6.0 \times 10^{24} \times 3.4 \times 10^{3}\right) /\left(6.4 \times 10^{6}\right) \times[1 / 3-1 / 4]$

C1

$=1.8 \times 10^{10} \mathrm{~J}$

A1

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13.4.3—The concept of gravitational potential leads to the gravitational potential question 1