Circular measure — practice question

The diagram depicts a cord looped around a pulley and a pin. The pulley is represented by a circle with centre $O$ and radius $5\text{ cm}$. The thickness of the cord and the dimensions of the pin $P$ may be ignored. The pin is placed $13\text{ cm}$ vertically beneath $O$. Points $A$ and $B$ lie on the circle so that $AP$ and $BP$ are tangents to the circle. The cord runs over the major arc $AB$ of the circle and beneath the pin so that the cord stays taut.