\(mV = (m + M){v_{{\rm{sys}}{\rm{.}}}}\)…(i)
If the system rises up to height h then by the conservation of energy \(\frac{1}{2}(m + M)v_{{\rm{sys}}{\rm{.}}}^{\rm{2}} = (m + M)gh\)…(ii)
==> \({v_{{\rm{sys}}{\rm{.}}}} = \sqrt {2gh} \)
Substituting this value in equation (i)
\(V = \left( {\frac{{m + M}}{m}} \right)\;\sqrt {2gh} \)