c
\(\begin{array}{l}
\,\,\,\,\,\,\,\,\,\,\,\,pseudo\,force\,or\,fictitious\,force,\\
{F_{fic}} = m\alpha \,Force\,of\,friction,\,f = \mu N = \mu m\alpha \\
The\,block\,of\,mass\,m\\
will\,not\,fall\,as\,long\,\\
as\,\\
\,\,\,\,\,\,\,\,\,\,\,\,\,f \ge mg\\
\,\,\,\,\,\,\,\,\,\,\mu m\alpha  \ge mg\\
\,\,\,\,\,\,\,\,\,\,\,\,\alpha  \ge \frac{g}{\mu }
\end{array}\)