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Homework Help: Fluid physics problem help

  1. Jan 10, 2005 #1
    I have the next problem:
    Water is falling from the H=1 m into the cylinder.
    Diametr of the culinder d=20 cm
    Q=dV/dt=100 (cm^3)/s (consumption of the water).
    I have to calculate force, which acts on the bottom of culinder in the end of 30nd second.

    I can't believe, that it is simply F=m*g (m=density*V; V=Q*t)! (here V- volume)
    Should I also take into acount dinamic pressure? Pdin=density*(v^2)/2; (here v-velocity) v=sqrt(2*g*H)
    F=m*g+pdin*S (S=pi*d^2/4 - area)
    Help me please!
  2. jcsd
  3. Jan 10, 2005 #2


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    Of course u'd need to include the force exerted by dinamical pressure.If u didn't,then the water would not be pouring into the cylinder,but instead being there motioness.

  4. Jan 10, 2005 #3
    In this way i receive:
    Pstatic=density*g*h1 (h1 - height of the water in the culinder)
    Pdinamic = density*(v^2)/2=desity*g*(H-h1) (From H falls the water)
    P=Pstatic+Pdin= density*g*H
    So it does not depend on the time and consumption of the water!!
    Is it really correct?
  5. Jan 11, 2005 #4
    Can anybody help? please
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