Rotational Motion

Two discs of moment of inertia \(I_1=4 \mathrm{~kg} \mathrm{~m}^2\) and \(I_2=2 \mathrm{~kg} \mathrm{~m}^2\), about their central axes & normal to their planes, rotating with angular speeds \(10 \mathrm{~rad} / \mathrm{s}\) & \(4 \mathrm{~rad} / \mathrm{s}\) respectively are brought into contact face to face with their axes of rotation coincident. The loss in kinetic energy of the system in the process is _________ J.