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Homework Help: Find initial velocity only need hint

  1. Jun 18, 2008 #1
    1. The problem statement, all variables and given/known data
    home run hit and baseball just clears the top of the bleachers.
    @= 35 degrees
    bleacher height = 21 meters
    distance from bleachers to home plate = 130 meters

    neglect air resistance

    find initial velocity and time of flight

    2. Relevant equations
    x comp:
    x= vcos@ t + at^2/2
    y comp
    y= vsin@ t + at^2/2
    vf^2= vi^2 + 2a(delta x)

    3. The attempt at a solution

    The thing is, in order to solve for velocity itd help to know the time and to solve for time itd help to know the velocity. So i thought i'd use vf^2= vi^2 + 2a(delta x) since it doesn't have time in the equation. I got
    0= (vi cos 35)^2 + 2(9.8) (130)
    i keep getting a negative inside the square root and im stuck.
    I just need a hint into the right direction, am i approaching this problem incorrectly?
  2. jcsd
  3. Jun 18, 2008 #2
    Careful now, you wouldn't have an acceleration in the x direction. Also, do you really think the final velocity would be zero? You really need to know what the equations mean and how vectors work. Remember, you have to do it component wise.

    So here's what you know: the distance in the y direction the ball travels, and the distance in the x direction that the ball travels. Two equations and two unknowns.
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