A disc shaped body (having a hole shown in the figure) of mass `m=10kg` and radius `R=10/9m` is performing pure rolling motion on a rough horizontal surface. In the figure point `O` is geometrical center of the disc and at this instant the centre of mass `C` of the disc is at same horizontal level with `O`. The radius of gyration of the disc about an axis pasing through `C` and perpendicular to the plane of the disc is `R/2` and at the insant shown the angular velocity of the disc is `omega=sqrt(g/R)` rad/sec in clockwise sence. `g` is gravitation acceleration `=10m//s^(2)`. Find angular acceleation `alpha` ( in `rad//s^(2)`) of the disc at this instant.