Energy, work and power — practice question

The diagram presents the vertical cross-section $ABC$ of a rough waterslide. Segment $AB$ is a straight line of length $5\,\text{m}$, making an angle $\theta$ with the horizontal, where $\sin\theta = 0.8$. Point $B$ is $2.5\,\text{m}$ above the level of $C$. A man of mass $80\,\text{kg}$, treated as a particle, slides down the waterslide from rest at $A$. The coefficient of friction between the man and the straight part of the waterslide is $0.1$.