Q: When a body rolls without sliding up an inclined plane, the frictional force is
(A) directed up the plane
(B) directed down the plane
(D) dependent on its velocity
Solution : Since the body rolls without sliding,
ap = 0 & vp = 0
Hence, v – rω = 0 & a – rα = 0
v = rω & a = rα
Since the body acceleration a is downwards parallel to the plane, therefore acceleration of the body must be in anticlockwise sense.
That means the friction must act up the plane to produce an anticlockwise torque to produce anticlockwise angular acceleration.