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After what time interval does the ball strike the ground

  1. Sep 21, 2007 #1
    1. The problem statement, all variables and given/known data
    A ball is thrown downward with initial speed of 8m/s from a height of 30m.

    2. Relevant equations
    \After what time interval does the ball strike the ground



    3. The attempt at a solution

    acceleration will equal -9.8m/s^2 because it's free fall
    would i use equation V=Vo-gt










    constant speed of a horse is 10m/s. distance from limb to saddle is 3m

    A) find horizontal distance between saddle and limb?
    B) for what time interval is he in the air?

    Attempted solution:
    X=Xo+Vo(t)+V2(a)(t^2)
    what equation do you use to find the time ... Yf=Yi+Vi(t)+1/2g(t^2) and rearange it to
     
  2. jcsd
  3. Sep 21, 2007 #2

    learningphysics

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    I'm confused. There seems to be two questions... one about a ball... about about a horse and saddle?
     
  4. Sep 22, 2007 #3
    sorry. it's two different problems
     
  5. Sep 22, 2007 #4

    learningphysics

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    This is the right equation to use for the first problem:

    Yf=Yi+Vi(t)+1/2g(t^2)

    but you need to be careful about directions and signs... you've taken downwards as positive here...
     
  6. Sep 22, 2007 #5

    HallsofIvy

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    Since you are NOT given the time but ARE given a distance, it would be better to use a distance formula: d= (1/2)gt2+ v0t. Donht forget that v0 is negative.








    This makes no sense to me at all. What does the "distance from saddle to limb" . At some paces some horses can go 10m/s while always having at least one foot on the ground- they are never "in the air".

    And what "limb"? A foreleg? Or is this a limb of a tree? Did you leave something out? is the horse jumping over a limb?
     
  7. Sep 22, 2007 #6
    yea i would use this formula
     
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