Newton's laws of motion — practice question

The diagram gives the vertical cross-section $OAB$ of a slide. The straight section $AB$ is tangent to the curve $OA$ at $A$. The line $AB$ makes an angle $\alpha$ with the horizontal, where $\sin \alpha = 0.28$. Point $O$ is $10\,\text{m}$ above $B$, and $AB$ is $10\,\text{m}$ long (see diagram). The section of the slide containing the curve $OA$ is smooth, whereas the section containing $AB$ is rough. A particle $P$ of mass $2\,\text{kg}$ is released from rest at $O$ and slides down the slide.