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Homework Help: Ball thrown off building

  1. Mar 4, 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 8.70 m/s at an angle of 22.0° below the horizontal. It strikes the ground 5.00 s later.
    Find the height from which the ball was thrown.


    3. The attempt at a solution
    i found final Velocity first: -8.70 + (-9.80)(5) and i got -57.7
    then i used this formula yf-yi = 1/2(Vy+Vi)t 1/2(-57.7 + -8.70)5
    to get 166 for the height, but it is wrong.
     
  2. jcsd
  3. Mar 4, 2010 #2
    The problem is that you took the entire initial velocity to be in the vertical direction, but the ball was thrown at an angle so in reality, part of that velocty is in the horizontal direction. You need to use the initial angle given and solve for the initial velocty in the y direction, and that's the velocity that will change due to gravity.
     
  4. Mar 5, 2010 #3
    thank you, that helped
     
  5. Mar 5, 2010 #4
    Try using some of the extra forumlas given for projectile motion, you can find them on wikipedia ect. they help alot, plus they're easier to use then 2D motion
     
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