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Homework Help: What is the inital speed of the ball?

  1. Oct 2, 2006 #1
    A ball player hits a home run and the baseball just clears a wall8.00m high located 142.0m from a home plate. The ball is hit at an angle of 40degrees to the horizontal and air resistance is negligible. Assume the ball is hit at a height of 1.1m above the ground. The acceleration of gravity is 9.81m/s^2. What is the inital speed of the ball?
  2. jcsd
  3. Oct 3, 2006 #2


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    Oh, come, on. Try. The vertical acceleration is -9.8 m/s2 and there is no horizontal acceleration. Taking v as the initial speed (what you want to find), the initial horizontal speed is v cos(40) and the initial vertical speed is v sin(40). Now find the horizontal and vertical speed functions, vx(t) and vy(t), and the horizontal length and vertical height functions, x(t) and y(t). When the ball passes over the the wall, you have x(t)= 142 and y(t)= 8. That gives you two equations for the two "unknowns", t and v.
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