Answer: Opposite to relative motion.
- A In direction of motion
- B Perpendicular to motion
- C Opposite to relative motion
- D Vertically downward
Correct answer: C. Opposite to relative motion
Explanation: Friction opposes relative motion between surfaces in contact.
Free-body diagram of a block on an incline: weight (mg) resolves into mg sinθ along the slope and mg cosθ into the slope, balanced by the normal force N and friction f.
Concept context
Newton's three laws, friction, circular motion, and free body diagrams.