Energy, work and power — practice question

The diagram depicts a wire $ABCD$ made up of a straight section $AB$ with length $5\,\text{m}$ and a section $BCD$ formed as a semicircle of radius $6\,\text{m}$ with centre $O$. The diameter $BD$ of the semicircle lies horizontally, while $AB$ is vertical. A small ring is placed on the wire and can move along it. It is released from rest at $A$. The section $AB$ of the wire is rough, so the ring has constant acceleration of $2.5\,\text{m s}^{-2}$ from $A$ to $B$.