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Homework Help: Power needed to keep velocity of conveyor belt constant

  1. Oct 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A conveyor belt travels at a constant velocity [tex]v[/tex] while sand is poured onto it at rate of [tex]\frac{dm}{dt}[/tex]. Find the power needed to drive the conveyor belt.


    2. Relevant equations
    [tex]P = \frac{dW}{dt} = F*v[/tex]
    [tex]F = m*\frac{dv}{dt}[/tex]


    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 [tex]\frac{dm}{dt}[/tex] into the equations.
     
  2. jcsd
  3. Oct 24, 2008 #2

    tiny-tim

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    Hi diablo2121! :smile:
    Noooo … [tex]F = \frac{d(mv)}{dt}[/tex] :wink:

    (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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