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

Options

A. `mu=(1)/(tanphi)`
B. `mu=(2)/(tanphi)`
C. `mu=2tanphi`
D. `mu=tanphi`

Answer

C