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Homework Help: Find the speed of the water

  1. Sep 9, 2004 #1
    Firemen are shooting a stream of water at a burning building using a high-pressure hose that shoots out the water with a speed of 25.0 m/s as it leaves the end of the hose. Once it leaves the hose, the water moves in projectile motion. The firemen adjust the angle of elevation [tex]\alpha[/tex]of the hose until the water takes 3.00 s to reach a building 45.0 m away. You can ignore air resistance; assume that the end of the hose is at ground level

    A.) Find the angle of elevation [tex]\alpha[/tex]
    B.) Find the speed of the water at the highest point in its trajectory.
    C.) Find the acceleration of the water at the highest point in its trajectory(magnitude of the acceleration).

    please help me start this, i have problems starting questions.

    what is "projectile motion"
    25.0 m/s is the initial velocity right? or is it the final velocity?

    for problem A.) how would i find the angle?
  2. jcsd
  3. Sep 9, 2004 #2


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    Your text should give you a good explanation of this basic concept. You can also try this page I googled just now.

    http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Vectors/ProjectilesMotion.html [Broken]

    the problem stated: "...shoots out the water with a speed of 25.0 m/s as it leaves the end of the hose."

    "as it leaves the end of the hose" would imply that it is the initial velocity. But just as an aside, it would also be the final velocity (don't worry about that right now though, you'll learn that when you get to energy conservation.)

    Since the water is undergoing projectile motion, you can simplify the problem by considering the horizontal and vertical components of its velocity. I don't want to give the solution away, but think of the data you are given in the problem: a distance, a velocity, and a time. Consider the horizontal component of the velocity using a little trig, and what you now know about projectile motion. This is all i'll tell you for now; draw out a diagram and think about it; if you still have difficulty, post again.
    Last edited by a moderator: May 1, 2017
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