I've been wondering after learning about rolling without slipping and how it needs static friction for an object to start rolling but my question is that if theoretically the surface is frictionless then due to the torque of the weight will the Cylinder keep rolling at a fixed place or slide down etc. Would appreciate a lot if I got to know what really happened as it's I don't seem to find much on the web.
Taking torque about COM of the disc. Torque due to mgsinα and mgcosα is zero. Only friction causes torque i.e. fR. Torque due to friction causes the rolling, hence in absence of friction there is no rotation which implies that disc won't be able to attain rolling condition.
The cylinder won't experience any torque, because gravity can be though of as acting at the cylinder's center and the normal force from the ramp points directly toward the center. So the cylinder's angular velocity won't change. If it is released without any rotation, then it will simply slide down the ramp without ever rotating.