The base of a hollow right cone of semi vertical angle ${30}^0$ is fixed to a horizontal plane. Two particles each of mass m are connected by a light and inextensible string which passes through a small hole in the vertex of the cone. One particle A hangs at rest inside the cone. The other particle B moves on the outer smooth surface of the cone at a distance $l$  from the vertex in a horizontal circle with center at A. neglecting friction and effect of sharp edge, the angular velocity of B is