Answer: 40 N.
- A 20 N
- B 30 N
- C 40 N
- D 50 N
Correct answer: C. 40 N
Explanation: Normal force = F. Friction = mu x F = 0.5F. For no sliding: 0.5F >= mg = 20. F >= 40 N.
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.