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Kinematics projectile motion problem

  1. Nov 30, 2009 #1
    1. The problem statement, all variables and given/known
    A ball is thrown from atop a 490m building with an initial velocity of 200m/s how far from the bottom of the building will it land


    2. Relevant equations
    d=vit+1/2at^2


    3. The attempt at a solution
    i have tried to put this in a equation and it was 490=-4.9 and it was 100 time is always multiplied by two to get x and it was 200 frm there i am confused
     
  2. jcsd
  3. Nov 30, 2009 #2
    For one thing, this problem requires TWO equations to solve. You need to find how long it takes for the ball to hit the ground, then find out how far it managed to get in that time.
     
  4. Dec 1, 2009 #3

    Redbelly98

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    Well, that equation does not give 490=-4.9. You have dropped t from the equation for no reason. Also, the vit term has disappeared.

    We know that the ball travels 490 m, the height of the building.
     
  5. Dec 2, 2009 #4
    I should have been more specific! The second step would be to find out how far in the horizontal direction the ball manages to get in that time.
     
  6. Dec 2, 2009 #5
    Now that I look more carefully, it's actually an ambiguous question. The problem doesn't say the direction in which the ball is thrown--is it straight up? Straight down? Straight away from the building? At a 45 degree angle? The answer definitely depends on the direction the ball is thrown.

    If I had to guess, I would say the throw was directly horizontal, since that's a much simpler problem and it seems more in line with where you seem to be in your physics education. Still, you should probably ask your prof. or teacher. Ambiguous questions are not OK!
     
  7. Dec 2, 2009 #6

    Redbelly98

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    Oops, I was interpreting the question as strictly vertical, and thought it asked how long it takes the ball to drop. My bad.

    It does appear that the 200 m/s initial velocity is in the horizontal direction. With no angle given, it would be either vertical or horizontal. But vertical would mean the ball simply lands at the base of the building; it would have to be horizontal for the problem to be meaningful.

    So ... initial velocity is 200 m/s in the horizontal direction. What then is the vertical component of the initial velocity?
     
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