Question

Cylinder rolling down an inclined plane direction of frictional force

Answer 1

Opposite to the direction of falling object.
1. Air provide frictional force.
2. Frictional Force. Of the surface.

Answer 2

Here the static friction must be determined.In case of rolling friction (in case of the asked question),the direction of frictional force will not be the same.It will be the Static friction which will be applied here.And the friction will help the cylinder rolling towards its way while falling through the inclined plane.So,the direction of cylinder's movement=the direction of static friction.