Probability — practice question

A light elastic string has a natural length of $4\text{ m}$ and modulus of elasticity $60\text{ N}$. A particle $P$ with mass $0.6\text{ kg}$ is fixed to the midpoint of the string. The string’s ends are fixed at points $A$ and $B$, which are on the same vertical line, with $A$ located $6\text{ m}$ above $B$. $P$ is projected vertically upwards from a point $2\text{ m}$ vertically above $B$. During the motion that follows, $P$ reaches instantaneous rest at a point $2\text{ m}$ below $A$.