Quick questions on Gravitational fields and potential energy: WACE Year 12 Physics Unit 3

The gravitational field strength at a point is the force per unit mass placed there:

Field lines show the direction a small test mass would be pushed and, by their spacing, the strength. Around a single planet the lines are radial and inward, spreading out with distance so the field weakens as $1/r^2$. Close to a small patch of surface the lines are nearly parallel and evenly spaced, which is why we treat the field as uniform for everyday problems.

When the field is treated as uniform, lifting a mass $m$ through a height $\Delta h$ changes its gravitational potential energy by

WACE often presents the energy story as graphs against position. For a mass dropped from rest, a graph of gravitational potential energy against height falls linearly (near a surface) while kinetic energy rises by the same amount, so the total mechanical energy stays a flat horizontal line, the signature of energy conservation with no losses. If the graph of total energy slopes downward, energy is being lost, usually to friction or air resistance as heat. Being able to read which curve is kinetic, which is potential and which is the conserved total, and to interpret a sloping total as a loss mechanism, is a recurring skill in extended-response questions.