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Defenestration homework not going so well -_-

  1. Sep 28, 2011 #1
    A ball is thrown horizontally from the top of
    a building 53.8 m high. The ball strikes the
    ground at a point 119 m from the base of the
    building.
    The acceleration of gravity is 9.8 m/s. The time (I got this answer and it's correct and all) is 3.3135sec.
    (part 2 of 4) Find the initial velocity of the ball.
    (part 3 of 4) Find the x component of its velocity just before it strikes the ground.
    007 (part 4 of 4) 10.0 points
    Find the y component of its velocity just before it strikes the ground.


    vaverage = d/t

    a = Vdelta/t

    vf = vi + at

    I don't even know any others -_-

    I tried to use vf^2 = vi^2 + 2ad??????? It didn't work. I am really lost but if someone could tell me which formula (kinematics) to use that would be great.


    I already got the time (part 1 of 4) to equal 3.3135sec but despite using the right equations etc I can't get the other three parts.
     
    Last edited: Sep 28, 2011
  2. jcsd
  3. Sep 28, 2011 #2

    gneill

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    Staff: Mentor

    The ball was thrown horizontally. How far did it travel horizontally? Over what time? What can change the horizontal velocity?

    What's its initial y-velocity? What could change the y-velocity?
     
  4. Sep 28, 2011 #3
    Accelerationg would change it, and I tried the answer (online homework) in both negative and positive?? The initial y-velocity goes unstated.
     
  5. Sep 28, 2011 #4

    gneill

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    Staff: Mentor

    Acceleration would change what in particular?

    The ball was thrown horizontally. What does that mean for the x and y components of the initial velocity?

    What equation describes the x-position with respect to time? How about the y-position?
     
  6. Sep 28, 2011 #5
    Acceleration would change the velocity only in the y-direction. Acceleration and therefore velocity in the x-direction remain constant, with accelerationx=0 m/s.

    [itex]\Delta[/itex]s=vit + .5 (a)(t2)

    Thanks so much!!!!!!!
     
  7. Sep 28, 2011 #6
    Actually that didn't work either -___-
     
  8. Sep 28, 2011 #7

    gneill

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    Staff: Mentor

    Didn't work for what? You'll have to be more specific. There are several parts to the problem. What are you trying to find first?
     
  9. Sep 28, 2011 #8

    berkeman

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    Staff: Mentor

    Sorry if I missed it. What's Defenestration?
     
  10. Sep 28, 2011 #9

    berkeman

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    Staff: Mentor

    Sorry if I missed it. What's Defenestration?
     
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