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Baseball: Rising and Falling speed

  1. Oct 14, 2009 #1
    1. The problem statement, all variables and given/known data

    A baseball is seen to pass upward by a window 28 m above the street with a vertical speed of 8 m/s. The ball was thrown from the street.

    (a) What was its initial speed?
    (b) What altitude does it reach?
    (c) How long after it was thrown did it pass the window?
    (d) After how many more seconds does it reach the street again?

    2. Relevant equations

    Vf = Vi + at
    Vf^2 = Vi^2 + 2ad
    d = Vi(t) + (.5)(a)(t)^2
    t = Vf/a or Vf-Vi/a



    3. The attempt at a solution

    So far I've only attempted a and c because I don't know how to go aout solving b or d.

    For a, I used the Vf^2 formula and changed it to equal Vi^2. So I had:

    2(a)(d) - Vf^2 = Vi^2 and with that I got 2(9.8)(28) - (8)^2 = Vi^2 and got 22

    I believe the problem may be with acceleration. Is it 9.8 when thrown uo, or only during free fall?


    For c, I took the answer i got from a, Vi = 22, and plugged it into the time equation. I did 8 - 22 / 9.8 to get 1.4 seconds.
     
  2. jcsd
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