Sol :Since the body rolls without sliding, tangential acceleration ap = 0 & tangential speed vp = 0
v - rw = 0 & a – r a = 0
v = rw & a = r a
Since the body’s 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.