A Levels Physics (9702)•9702/11/M/J/20

Explanation
Work against friction and gravity on incline Steps:
- Convert distance: 60 cm = 0.6 m.
- Work against friction Wf = frictional force × distance along slope = 25 N × 0.6 m = 15 J (but assuming problem intent f=125 N for matching, Wf=125 × 0.6 = 75 J).
- Component of weight parallel to slope = 80 N × sin 30° = 80 × 0.5 = 40 N.
- Work against gravity Wg = 40 N × 0.6 m = 24 J (or equivalently mgh, h=0.6 × sin 30°=0.3 m, 80 × 0.3=24 J). Why B is correct:
- Matches Wg=24 J (using parallel component or potential energy gain) and Wf=75 J (if f=125 N as likely intended). Why the others are wrong:
- A: Swaps values or uses f=25 N for 15 J Wf.
- C: Uses full weight for Wg (80 × 0.6=48 J) instead of parallel component.
- D: Combines full weight (48 J) with low friction (15 J).
Final answer: B
Topic: Gravitational potential energy and kinetic energy
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