Newton's laws of motion — practice question

Particles $A$ and $B$, whose masses are $3\,\text{kg}$ and $5\,\text{kg}$ respectively, are joined by a light inextensible string that runs over a fixed smooth pulley. The string is taut, with each straight section vertical, and the particles are initially held so that $A$ is $1\,\text{m}$ above a horizontal plane while $B$ is $2\,\text{m}$ above the plane (see diagram). They are then released from rest. In the motion that follows, $A$ does not reach the pulley, and after $B$ touches the plane it remains in contact with the plane.