Q: Sand is being dropped on a conveyor belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of v m/s will be
(a) Mv/2 newton
(b) Zero
(c) Mv newton
(d) 2 Mv newton
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Ans: (c)
Sol: Force = change in momentum per sec
$ \displaystyle F = v \frac{dm}{dt} $
F = v × M