Kinematics of motion in a straight line — practice question

Particles $P$ and $Q$ are connected at the two ends of a light inextensible string that passes over a fixed smooth pulley. The system is released from rest, with the string taut, the straight sections vertical, and both particles $2\,\text{m}$ above horizontal ground. $P$ moves vertically downwards and does not rebound when it reaches the ground. At the moment that $P$ reaches the ground, $Q$ is at point $X$, from where it continues to move vertically upwards without reaching the pulley. Given that $P$ has mass $0.9\,\text{kg}$ and that the tension in the string is $7.2\,\text{N}$ while $P$ is moving, find