Probability — practice question

A particle $P$ with mass $0.1\,\text{kg}$ is fastened to one end of a light inextensible string of length $0.5\,\text{m}$. The other end of the string is fixed at point $A$. Particle $P$ travels round a circle whose centre $O$ lies on a smooth horizontal surface $0.3\,\text{m}$ below $A$. The string tension has magnitude $T\,\text{N}$ and the magnitude of the force exerted on $P$ by the surface is $R\,\text{N}$.