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Homework Help: Fireman Roof Problem

  1. Oct 23, 2006 #1
    A fireman shoots water out of a hose at 12m/s. he is standing on a 20m high roof and is aiming for the top of another roof at the same height, but it is 21 m away. What angle should the fireman aim the hose above the horizontal in order to hit the other roof?

    i set up a chart but have no idea what to do now:
    x y
    vi " '
    vf " -'
    a 0 -9.8
    d 21 0
  2. jcsd
  3. Oct 23, 2006 #2


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    Staff Emeritus
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    Gold Member

    You need to split up the trajectory into horizontal and vertical components, start by writing down the following;

    • Initial Horizontal Velocity*
    • Initial Vertical Velocity*
    • Change in Vertical Displacement
    • Change in Horizontal Displacement
    • Acceleration in the vertical plane

    Note that (*) will be trigonometric functions of the launch angle. Once you have done this, apply kinematic equations to each component independently.
  4. Oct 23, 2006 #3
    In questions about projectiles, it is quite often, like in this case that you will need to find the time by resolving it vertically.
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