c
\(\begin{array}{l}
\,\,\,\,\,\,\,\,\,\,\,\,F = \frac{d}{{dt}}\left( {Mv} \right) = v\frac{{dM}}{{dt}} + M\frac{{dv}}{{dt}}\\
As\,\,v\,\,is\,a\,{\rm{constant,}}\\
\,\,\,\,\,\,\,\,\,\,\,\,F = v\frac{{dM}}{{dt}}.\,\,\,\,\,\,\,\,But\frac{{dM}}{{dt}} = Mkg/s\\
\therefore \,To\,keep\,the\,conveyer\,belt\,moving\,at\\
v\,m/s,\,force\,needed\, = vM\,newton.
\end{array}\)