Q 11-04-027JEE MainEAMCET 2013 (Engineering)Hard
The upper half of an inclined plane of inclination $\theta$ is perfectly smooth while the lower half is rough. A block starting from rest at the top of the plane will again come to rest at the bottom. The coefficient of friction between the block and the lower half of the plane is given by
Answer: (A) $\mu = 2\tan\theta$
Concept. Starts and ends at rest: work by gravity over $2L$ $=$ work against friction over $L$.
Step 1. Equation. $mg\sin\theta(2L) = \mu mg\cos\theta(L)$.
Step 2. Solve. $\mu = 2\tan\theta$.
Answer. $\mu = 2\tan\theta$ (Option A).
Solution by Sreeraj P, M.Sc Physics