A solid cylinder of mass $\mathrm{m}$ and radius $\mathrm{r}$ is rolling down on a rough inclined plane of inclination $\mathrm{\theta }$. The coefficient of friction between the cylinder and incline is $\mathrm{\mu }$. Then

Only maximum frictional force is $\mu mg \cos \theta$

Since point of action of frictional force is not moving ,work done by it is zero .

Direction of frictional force is up the inclined plane .

$\mathrm{f}=\frac{\mathrm{mg} \sin \mathrm{\theta }}{1+{\displaystyle \frac{{\mathrm{mR}}^2}{\mathrm{I}}}}$