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Homework Help: Minimum velocity

  1. Feb 3, 2010 #1
    1. The problem statement, all variables and given/known data

    a fire hose is turned on the door of a burning building in order to knock the door down. This requires a force a 1000 N. if the hose delivers 40 kg per second, what is the minimum velocity of the stream needed? assuming the water doesn't bounce back?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 4, 2010 #2
    Although you did not show your attempt clearly, it would help if you thought a thousand newton of force as 1000 kg-m/s momentum gained/lost per second. Since water does not bounce back, it loses all momentum on the door and hence exerts a force.The rate of flow of water is given so could you find force it would exert on the door assuming velocity to be v?
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