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Homework Help: A ball being shot from level ground with a twist

  1. Oct 15, 2012 #1
    Not a literal twist! It's just a bit more complex.
    1. The problem statement, all variables and given/known data

    A ball is to be shot from level ground toward a wall at a distance "x". I am given the graph of the y component of velocity just as it would reach the wall, as a function of that distance x(m). Here's the equation of the line:y=-.5x+5, [0, 20]
    What is the launch angle?

    2. Relevant equations
    v = vo +at
    x = xo + Vot + .5at2
    v2 = (vo)2 + 2a(x - xo)

    3. The attempt at a solution

    So I wrote out all I knew about the x and y components
    y: vo = 5, a = -9.8, xo = 0
    x: a=0

    I attempted to created a triangle of the horizantal and vertical components of velocity and the initial velocity as the hypotenuse solve with trig. I got
    sin(θ)= (5)/(V)
    tan(θ)= (5)/(vox)
    No help.
    I really am stuck! Using kinematics, you cant find the initial velocity because you don't know the time. You can't find the time, because you don't know where in the 20 m of the trajectory the ball hit the wall (according to my interpretation of the problem) Ah! If you could help I would be so grateful!!
    Thank you so much!!!
    Last edited: Oct 15, 2012
  2. jcsd
  3. Oct 15, 2012 #2
    x depends on time. Use this dependency.
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