The upper half of an inclined plane with inclination $\phi$ is perfectly smooth while the lower half is rough. A body starting from rest at the top will again come to rest at the bottom if the coefficient of friction for the lower half is given by\\
(1) $2\sin\phi$\\
(2) $2\cos\phi$\\
(3) $2\tan\phi$\\
(4) $\tan\phi$