A ring of mass m free to slide on a fixed smooth horizontal wire is attached to one end of a string of length $60 cm$. The other end of the string is attached to a particle of mass $2m$. The ring and the particle are initially held at the same horizontal level with the string taut. If the system is now released, find the angular velocity of the string when it makes an angle of $60°$ with the vertical.  (round off the answer to nearest integer)