Probability — practice question

A particle $P$ with mass $0.7\,\text{kg}$ is connected by a light elastic string to a fixed point $O$ on a smooth plane that is inclined at $30^\circ$ to the horizontal. The string’s natural length is $0.5\,\text{m}$ and its modulus of elasticity is $20\,\text{N}$. Particle $P$ is launched up the line of greatest slope through $O$ from a point $A$ below the level of $O$. Initially, the kinetic energy of $P$ is $1.8\,\text{J}$ and the elastic potential energy stored in the string is also $1.8\,\text{J}$.