A uniform rod of mass m is placed at right angles to a smooth plane of inclination $\alpha$ with one end in contact with it. The rod is then released. Find reaction of the plane when the inclination to the plane is $\phi$ .
The solution in the book says that there is no force acting along the plane and thus there will not be any movement of centre of gravity in that direction. Isn't this incorrect because $mg\sin\alpha$ is acting in that direction ?