Probability — practice question

A particle $P$ with mass $0.3\,\text{kg}$ travels round a circle centred at $O$ on a smooth horizontal surface. $P$ is connected to $O$ by a light elastic string of modulus of elasticity $12\,\text{N}$ and natural length $l\,\text{m}$. The particle moves at $4\,\text{m s}^{-1}$, and the radius of its circular path is $2l\,\text{m}$.