Sand is being dropped on a conveyor belt at the rate of M kg/s. The force(in Newton) necessary to keep the belt moving with a constant velocity of v m/s will be

$\frac{Mv}{2}$ 0 Mv 2Mv

Mv

From newtons second law of motion F = $\frac{dP}{dt}$ ⇒ F = $\frac{d(mv)}{dt} = m\frac{dv}{dt} + v\frac{dm}{dt}$ since velocity is constant $m\frac{dv}{dt}$ = 0 ⇒ F = v$\frac{dm}{dt}$ = Mv since $\frac{dm}{dt}$ = M