Newton's laws of motion — practice question

Particles $A$ and $B$, with masses $0.3\,\text{kg}$ and $0.7\,\text{kg}$ respectively, are joined to the two ends of a light inextensible string. Particle $A$ is initially at rest on a rough horizontal table, and the string passes over a smooth pulley fixed at the table edge. The coefficient of friction between $A$ and the table is $0.2$. Particle $B$ hangs vertically below the pulley, with its height $0.5\,\text{m}$ above the floor (see diagram). The system is released from rest, and $0.25\,\text{s}$ later the string breaks. In the later motion, $A$ does not reach the pulley.