\(\begin{array}{l}
\therefore \,0 = V - at\,\,or,\,\, - a = \frac{{0 - V}}{t} = - \frac{V}{t}\\
\,\,\,\,f = \mu R = \mu mg\,\left( {f\,is\,the\,force\,of\,friction} \right)\\
\therefore {\rm{Retardation,}}\,{\rm{a}}\,{\rm{ = }}\mu {\rm{g}}\,\therefore {\rm{t}}\, = \frac{V}{a} = \frac{V}{{\mu g}}.
\end{array}\)