Q. The upper half of an inclined plane of inclination $\theta$ is perfectly smooth while the lower half is rough. A body starting from the rest at top comes back to rest at the bottom if the coefficient of friction for the lower half is given by

A) $\mu = \sin\theta$
B) $\mu = \cot\theta$
C) $\mu = 2\cos\theta$
D) $\mu = 2\tan\theta$
Explanation

(d) For upper half
$v^{2} = u^{2} + 2al/2 = 2\left( g\sin\theta \right)l/2 = gl\ sin\ \theta$
For lower half
$\Rightarrow 0 = u^{2} + 2g(\sin{\theta - \mu\cos\theta)\ \frac{l}{2}}$
$\Rightarrow - gl\sin\theta = gl(\sin\theta - \mu\cos\theta)$
$\Rightarrow \mu\cos\theta = 2\sin\theta \Rightarrow \mu = 2\tan\theta$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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