Question Detail
Question
A block of mass m is placed on an inclined plane. The angle of the incline is gradually increased until the block is just about to slip. At this critical angle θs, the coefficient of static friction μs is equal to:
Correct Answer
Option D is the correct answer.
Detailed Explanation
At the point of slipping, the force pulling the block down the incline (mg sin θs) equals the maximum static frictional force (μs mg cos θs). Setting them equal gives mg sin θs = μs mg cos θs, so μs = tan θs.
Hint
Divide both sides of the equilibrium equation by mg cos θs.