Probability — practice question

The diagram depicts a smooth, narrow tube bent into a fixed vertical circle with centre $O$ and radius $0.9\,\text{m}$. One end of a light elastic string, whose modulus of elasticity is $8\,\text{N}$ and natural length is $1.2\,\text{m}$, is fastened to the top point $A$ on the inside of the tube. The opposite end is attached to a particle $P$ of mass $0.2\,\text{kg}$. The particle is released from rest at the lowest point on the inside of the tube. Using energy, calculate