Two cases as shown in the figures $($a$)$ and $($b$),$ the identical drum of mass $20$ kg rotates under the load $($a$)$ a constant force $P=50N$ and; $($b$)$ a kettle of weight $W=50N.$ If both the drums are released from rest, determine a$)$ the velocity of the kettle after $8s$;$b)$ angular velocity of the drum under the constant force $50$ N after $8$ s $.$ The radius of gyration of the drum about its axis of rotation is $175$ mm and the radius of the drum is $200$ mm $.$