A round disc of moment of inertia $$I$$₂ about its axis perpendicular to its plane and passing through its centre is placed over another disc of moment of inertia $$I$$₁ rotating with an angular velocity $$\omega $$ about the same axis. The final angular velocity of the combination of discs is

Three particles, each of mass m gram, are situated at the vertices of an equilateral triangle ABC of side $$l$$ cm (as shown in the figure). The moment of inertia of the system about a line AX perpendicular to AB and in the plane of ABC, in gram-cm² units will be

A wheel having moment of inertia 2 kg m² about its vertical axis, rotates at the rate of 60 rpm about this axis. The torque which can stop the wheel's rotation in one minute would be

The ratio of the radii of gyration of a circular disc about a tangential axis in the plane of the disc and of a circular ring of the same radius about a tangential axes in the plane of the ring is