The upper half of an inclined plane with inclination
Question:

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. $\tan \phi$

Correct Option: , 3

Solution: