Power needed to keep velocity of conveyor belt constant

1. Oct 23, 2008

diablo2121

1. The problem statement, all variables and given/known data
A conveyor belt travels at a constant velocity $$v$$ while sand is poured onto it at rate of $$\frac{dm}{dt}$$. Find the power needed to drive the conveyor belt.

2. Relevant equations
$$P = \frac{dW}{dt} = F*v$$
$$F = m*\frac{dv}{dt}$$

3. The attempt at a solution
I have the equations needed to solve the problem, but I'm confused as to how I can translate $$\frac{dm}{dt}$$ into the equations.

2. Oct 24, 2008

tiny-tim

Hi diablo2121!
Noooo … $$F = \frac{d(mv)}{dt}$$

(this is the full version of Newton's second law … f = m dv/dt is only a special case, valid only when dm/dt = 0)

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