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Homework Help: Projectile Motion Horizontal Displacement Equation

  1. Sep 18, 2008 #1
    The problem statement, all variables and given/known data

    A fire hose held near the ground shoots water at a speed of 7.5 m/s. At what angle(s) should the nozzle point in order that the water would land 3.0 m away?

    The attempt at a solution

    I remember from engineering there was a single equation you could use to find the horizontal displacement of an object given its initial velocity and projected velocity. I tried deriving it and came up with this:

    x = (2(vi)2sin2[theta])/19.6

    Could somebody please confirm this?

    It also asks: Why are there two different angles? I know how to describe this logically, but my teacher usually prefers a more mathematical answer. Would I just say that there are two values for theta that yield the same sine value?
  2. jcsd
  3. Sep 18, 2008 #2


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    Hi ArbazAlam! :smile:

    (have a theta: θ)

    Yes, that's right. :smile:

    (though why didn't you just say x = (vi)2sin2θ/9.8 ? :wink:)

    Yup … that would do … you could even say how the two values are related! :wink:
  4. Sep 18, 2008 #3
    Thank you! I didn't even notice those units canceled out. And thank you for the theta.
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