Two discs A and B are mounted coaxially on a vertical axle. The dics have moments of inertia I and 2I respectively about the common axis. Disc A is imparted an initial angular velocity `2omega` using the entire potential energy of a spring compressed by a distance `x_1.` Disc B is imparted an angular velocity `omega` by a spring having the same spring constant and compressed by a distance `x_2.` Both the discs rotate in the clockwise direction.

When disc B is brought in contact with disc A, the acquire a common angular velocity in time t. The average frictional torque on one disc by the other during this period is