Energy, work and power — practice question

Particles $P$ and $Q$, with masses $2.5\text{ kg}$ and $0.5\text{ kg}$ respectively, are joined by a light inextensible string that runs over a small smooth pulley fixed at the top of a plane inclined at an angle of $30^\circ$ to the horizontal. $P$ rests on the plane while $Q$ hangs below the pulley, with $Q$ initially $2\,\text{m}$ lower than $P$ in level (see diagram). $P$ is let go from rest with the string taut and moves down the plane. The plane is rough, and the coefficient of friction between the plane and $P$ is $0.2$.