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Initial velocity of a Ball thrown up

  1. Sep 30, 2009 #1
    Can someone one show me a step by step example of how to work out a problem where a ball is thrown up and it is a catched after lets say 10.5s, so how would I find out the initial velocity?
     
  2. jcsd
  3. Sep 30, 2009 #2

    tiny-tim

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    Welcome to PF!

    Hi simpleee! Welcome to PF! :wink:

    You have s t and a, and you want to find u …

    which of the usual constant acceleration equations do you think will help here? :smile:
     
  4. Sep 30, 2009 #3
    truthfully, im not quiet sure.
    I need help understanding which one to use and why exactly I should use it.
    s = ut + 1/2 at squared
     
  5. Sep 30, 2009 #4
    Oh and thank you for the welcome. =]
     
  6. Sep 30, 2009 #5

    tiny-tim

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    (try using the X2 tag just above the Reply box :wink:)

    ok … there's only three constant acceleration equations, each with four variables, so you just chose the equation with the four variables that you're interested in.

    In this case, you have s t and a, and you want to find u, so you choose s = ut + 1/2 at2 because it has all of them. :smile:
     
  7. Sep 30, 2009 #6
    but i only have 10.5s and 9.8 for gravity.
    So how would i know the rest?
     
  8. Sep 30, 2009 #7

    tiny-tim

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    u = 10.5, a = -9.8, and s = 0 (I'm assuming that the person catches it at the same height that (s)he throws it from :wink:).
     
  9. Sep 30, 2009 #8
    0 = 10.5 t + 1/2 9.8 t2
    0 = 10.5 - 4.9 t2
     
  10. Sep 30, 2009 #9

    tiny-tim

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    You mean 0 = 10.5 - 4.9 t …

    yes, that's right. :smile:
     
  11. Sep 30, 2009 #10
    Do I get the t by itself now?
    I think I might have posted this on the wrong section. .-.
     
  12. Sep 30, 2009 #11

    tiny-tim

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    Yes … t = 10.5/4.9. :smile:
    That happens quite a lot here! :biggrin:
     
  13. Sep 30, 2009 #12
    Why did it turn into 10.5/4.9?
    Is there any rules on how many times we can ask for help? o.o
     
  14. Sep 30, 2009 #13

    tiny-tim

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    0 = 10.5 t - 1/2 9.8 t2

    so 0 = 10.5 - 4.9 t

    so 10.5 = 4.9t

    so t = 10.5/4.9 :smile:
    You have to keep asking until you understand it! :biggrin:
     
  15. Sep 30, 2009 #14
    Good, good.
    All the better! ^_^
    2.1m/s?
     
  16. Nov 10, 2009 #15
    I guess this problem depends on how strong your esophagus is.

    -rlv.zazzle.com-awesome_smiley_photo_sculpture_photosculpture-p153359710604909267220_210.jpg
     
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