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Homework Help: Momentum - Jet of water

  1. Feb 25, 2010 #1
    1. The problem statement, all variables and given/known data

    A jet of water has a diameter of 30mm and a velocity of 40m/s. Determine the momentum/sec of the water. (Take p to be 10000kg/m3)

    this is my first post, apologies if i have missed anything out...
  2. jcsd
  3. Feb 25, 2010 #2
    Welcome to Physics Forums!

    You need to show us some attempt at a solution, and tell us what exactly it is you don't understand, before we can help you?
    Do you know the formula for momentum?
  4. Feb 25, 2010 #3
    Ah ok, to be honest i'm fairly lost. Most of the problems i've encountered so far have been to do with impact m1u1+m2u2=(m1+m1)v etc...

    i'm not exactly looking for the answer, but perhaps a nod in the right direction :-)
  5. Feb 25, 2010 #4
    If you think of the jet of water as a cylinder of water, what volume of water passes in one second? You have the radius/diameter of the end and you know how long the cylinder is from the speed of the jet.
  6. Feb 25, 2010 #5
    Yeah i thought of it that way but then hit a wall...

    so the volume is pi*0.015^2*40 = 0.0283m^3 * 1000 = 28.3kg

    then is it 28.3 * 40 to get 1132kgms-1 ? is there another step i'm missing?
  7. Feb 25, 2010 #6
    That's it. That is the "mv" in one second.
    Well done.
  8. Feb 26, 2010 #7
    thanks for your help dude
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