A sphere of mass m, moving with velocity V, enters a hanging bag of sand and stops. If the mass of the bag is M and it is raised by height h, then the velocity of the sphere was

By the conservation of linear momentum 
Initial momentum of sphere 
= Final momentum of system 
$mV=(m+M)v_{\text{sys.}} \dots \left(i\right)$
If the system rises up to height h then by the conservation of energy 

$\frac{1}{2}(m+M)v_{\text{sys.}}^{\text{2}}=(m+M)gh\dots \left(ii\right)$
$\Rightarrow v_{\text{sys.}}=\sqrt{2gh}$
Substituting this value in equation (i) 
$V=\left(\frac{m+M}{m}\right)\sqrt{2gh}$