The upper half of an inclined plane of inclination is perfectly smooth while the lower half 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
Suppose length of plane is L. When block descends the plane, rise in kinetic energy = fall in potential energy
= mg Lsin
Work done by friction
= x (Reaction) x Distance
Now, work done = change in KE
= 2 tan