Q: A cylinder rolls up an inclined plane, reaches some height and then rolls down (without slipping throughout these motions). The directions of the frictional force acting on the cylinder are
(a)Up the incline while ascending and down the
incline while descending
(b)Up the incline while ascending as well as
descending
(c)Down the incline while ascending and up the
incline while descending
(d)Down the incline while ascending as well as
descending
Ans: (b)
Sol: The component of weight m g sinθ is always down the plane whether it is rolling up or rolling down . Therefore for no slipping , the sense of angular acceleration should also be same in both the cases . Therefore force of friction always act upwards .