A test car on a rollercoaster track travels along a section of track containing four sensor gates: PPP, QQQ, RRR, and SSS.
The coordinate profile of the track is shown in the figure below, where x x\,x represents the horizontal position and y y\,y represents the vertical height above a reference level.

The coordinates of the gates are:
| Sensor Gate | Horizontal position, x (m)x\text{ (m)}x (m) | Vertical height, y (m)y\text{ (m)}y (m) |
|---|---|---|
| PPP | 10 | 20 |
| QQQ | 40 | 50 |
| RRR | 75 | 15 |
| SSS | 100 | 42 |
Between which two sensor gates does the test car experience the greatest overall change in gravitational potential energy?
Between PPP and QQQ
Between QQQ and RRR
Between RRR and SSS
Between PPP and SSS