Probability — practice question

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