Answer: Static friction balances the applied force.
- A The applied force exceeds the maximum static friction limit
- B The normal reaction force exactly cancels the applied force
- C Static friction balances the applied force
- D The surface has zero coefficient of friction
Correct answer: C. Static friction balances the applied force
Explanation: Block stays at rest because static friction adjusts to exactly balance the applied force, up to its maximum value.
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.