The two wheels have the similar mass and radius of 4.7 kg and 0.42 m, correspondingly. One has (i) the shape of a hoop and other (ii) the shape of a solid disk. The wheels begin from rest and encompass a constant angular acceleration with respect to the rotational axis which is perpendicular to the plane of the wheel at its center. Each turns via an angle of 14 rad in 8.4 s. Find out the total external torque which acts on each wheel.