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Homework Help: Horizontal range of a projectile

  1. Apr 20, 2010 #1
    1. The problem statement, all variables and given/known data

    A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 7.80 m/s at an angle of 15.0° below the horizontal. It strikes the ground 6.00 s later.
    (a) How far horizontally from the base of the building does the ball strike the ground?

    2. Relevant equations

    Vx = xsinTheta

    DeltaX = Vx . t

    3. The attempt at a solution

    Vx = 7.8sin(15) = 2.02 m/s^-1

    DeltaX = (2.02)(6) = 12.11m

    Something is seriously wrong in my answer although I can't see what. The answer should be 45.2m.
  2. jcsd
  3. Apr 20, 2010 #2
    I realize I am using Vx = xsinTheta instead of Vx = xcosTheta, although why is it that? When drawing a triangle of this and doing the trig, I get the first equation, could someone please explain this.
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