Probability — practice question

A light inextensible string of length $1.2\text{ m}$ is fixed at one end to a point $O$ on a smooth horizontal surface. Particles $P$, $Q$ and $R$ are attached to the string so that $OP = PQ = QR = 0.4\text{ m}$. They move in horizontal circles about $O$ with constant angular speed $\omega\text{ rad s}^{-1}$, with $O$, $P$, $Q$ and $R$ all lying on one straight line (see diagram). $R$ has mass $0.2\text{ kg}$, and the tensions in the two sections of string connected to $Q$ are $6\text{ N}$ and $10\text{ N}$.