Probability — practice question

A particle $P$ with mass $0.7\,\text{kg}$ is connected to a fixed point $O$ by a light elastic string whose natural length is $0.6\,\text{m}$ and whose modulus of elasticity is $15\,\text{N}$. Particle $P$ is projected vertically downward from $A$, where $A$ is $0.8\,\text{m}$ vertically beneath $O$. The initial speed of $P$ is $2\,\text{m s}^{-1}$.