A cord is wrapped on a pulley (disc) of mass M and radius R as shown in the figure. To one end of the cord, a block of mass M is connected as shown and to other endin (a) a force of 2 Mg and in (b) a block of mass 2M. Let angular acceleration of the disc in (a) and (b) is αA and αB, respectively, then (cord is not slipping on the pulley).