Answer: Different objects.
- A Same object in opposite directions
- B Different objects
- C Same object in same direction
- D Adjacent objects only
Correct answer: B. Different objects
Explanation: Action-reaction pairs act on different bodies. They never cancel each other because they act on different objects.
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.