Q. A cylinder roll up an inclined plane, reaches some height and then rolls down (without slipping throughout these motions). The directions of frictional force acting on the cylinder are
A) Up the inclined 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
Explanation
(a) As shown in figure, component of weight ($mg\sin\theta$) is always down the inclined plane, whether the cylinder is following up or it is rolling down. Therefore, for no slipping, sense of angular acceleration must be the same in both the cases. Therefore, force of friction ($f$) acts up the inclined plane in both the cases
[image:5_image237.emf]
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.