A uniform cylinder of mass M and radius R is to be pulled over a step of height a a   < R by…

A uniform cylinder of mass $\mathrm{M}$ and radius $\mathrm{R}$ is to be pulled over a step of height a $\left(\mathrm{a} <\mathrm{R}\right)$ by applying a force $\mathrm{F}$ at its centre  $\text{'}\mathrm{O}\text{'}$ perpendicular to the plane through the axes of the cylinder on the edge of the step (see figure). The minimum value of $\mathrm{F}$ required is :