From Mechanics

The maximum value for the speed \displaystyle v is determined by the maximum value which the frictional force \displaystyle Fcan assume which is:

\displaystyle F=\mu R gives

\displaystyle \begin{align} & m\frac{{{v}^{2}}}{r}=\mu mg \\ & v=\sqrt{\mu rg}=\sqrt{0\textrm{.}8\times 140\times 9\textrm{.}8}=33\textrm{.}1\text{ m}{{\text{s}}^{\text{-1}}} \\ \end{align}