# 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 if the coefficient of friction between the block and the lower half of the plane is given by
$\begin{array}{1 1}\mu=2\tan\theta\\\mu=\tan\theta\\\mu=\large\frac{2}{\tan\theta}\\\mu=\large\frac{1}{\tan\theta}\end{array}$