Probability — practice question

A particle $P$ has mass $0.2\,\text{kg}$ and is joined to fixed point $A$ by a light inextensible string of length $0.4\,\text{m}$. A second light inextensible string, of length $0.3\,\text{m}$, links $P$ to fixed point $B$, which lies vertically beneath $A$. The particle $P$ travels in a horizontal circle whose centre lies on the line $AB$, and $\angle APB = 90^\circ$ (see diagram).