A cylinder rolls up an inclined plane, reaches some height and then rolls down (without slipping thoughout these motions) .The directions of the firctional force acting on the cylinder are

Options

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

Answer

B

Explanation

For pure rolling, `V=omegaR`. While going up, v decreases so friction acts up the incline to decrease `omega`. While going down, V increases. So friction acts up to increase `omega`.

`therefore` The frictionless force, acting on the cylinder, is always up the incline, while ascending as well as descending.