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Homework Help: Force to hold nozzle with given flow rate and velocity

  1. Mar 30, 2010 #1
    1. The problem statement, all variables and given/known data

    A fire hose discharges water at a rate of 16.0 kg/s with a speed of 20 m/s. What magnitude of force is needed to hold the nozzle stationary?

    2. Relevant equations

    Impulse= Change in Momentum, Momentum (p)= mv, velocity final=velocity inital + at

    3. The attempt at a solution

    V= 20m/s + 9.81m/(s*s)= 29.81

    Since impulse is the force over time, I thought impulse should be the force needed to keep the hose stationary, but it's not. Any help in where I went wrong would be great! Thanks!
  2. jcsd
  3. Mar 30, 2010 #2
    Re: Impulse-Momentum

    Well, first of all I don't see why you're calculating in gravity. Remember, you're only interested in the force as soon as it exits the fire hose.

    So, the momentum would just be the mass discharged per second times the velocity of the discharged mass (16*20)

    I took the beginning of physics froma really bad teacher and as such spent my calss time talking to my girlfriend and ignoring the class, so I'm fuzzy but it seems that that should be your answer.
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