6. A tangential force of 20N is acting on a rotating disc as shown in the figure. The radius and moment of inertial of the disc are 0.2m and 4 Kgm² respectively. If the disc starts to rotate from rest.

a. (8 points)

What is the torque acting on the disc? Calculate the angular acceleration of the disc.

b. (7 points)

What is the angular velocity of the disc after 4s?