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2d Kinematics

  1. Oct 23, 2006 #1
    A baseball leaves a pitcher's hand horizontally at a speed of 165 km/h. The distance to the batter is 18.3 m. Neglect air resistance.

    (a) How long does it take for the ball to travel the first half of that distance?
    s
    (b) How long does it take for the ball to travel the second half of that distance?
    s
    (c) How far does the ball fall under gravity during the first half?
    m
    (d) How far does the ball fall under gravity during the second half?
    m

    For A I know D and V so I just did v = d/t which translates to t = d/v

    It doesnt work.. What am I doing wrong?
     
    Last edited: Oct 23, 2006
  2. jcsd
  3. Oct 23, 2006 #2

    radou

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    I suggest you write down the equations for projectile motion. It might be useful to type 'baseball' or 'projectile motion' into the search box, since this is a typical kinematics problem which appears very often here. :smile: Anyway, present some of your work, and we'll be glad to help.
     
  4. Oct 23, 2006 #3
    :) I did t = d/v which is

    Well ask for the time for the first half of the distance of the thrown ball..

    So 18.3/2 = 9.15

    then t = d/v
    t = 9.15/165
    Which = .05545 and that is wrong.
     
  5. Oct 23, 2006 #4
    Oh I think I have to convert from km/h to m/s right?
     
  6. Oct 23, 2006 #5

    radou

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    Yes, of course. Watch out for the units.
     
  7. Oct 23, 2006 #6
    Well I did it

    165km/h = 45.833 m/s

    so t = 9.15/45.833..Which gets you .1996 and that is still wrong.
     
  8. Oct 23, 2006 #7
    t = s/v What's S?
     
  9. Oct 23, 2006 #8

    radou

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    Oooops, I deleted my last post, because I wrote something stupid, please ignore it. I'm trying to figure this out right now.
     
  10. Oct 23, 2006 #9
    Oh, alright.
     
  11. Oct 24, 2006 #10
    So anyone?
     
  12. Oct 24, 2006 #11

    OlderDan

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    Except for the lack of units, this is not wrong. Did you state the problem correctly?
     
  13. Oct 24, 2006 #12
    Nvm, that is right. I was just being stupid and typing it in the wrong box. So a and b are solved, I'm going to try C now.
     
  14. Oct 24, 2006 #13
    So

    A = .1996
    B = .1996
    C = .1952
    D = ?

    I tried doubling my time and just doing .5(-9.8)(.3992^2)

    And got -.78086 Which is incorrect.
     
  15. Oct 24, 2006 #14

    radou

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    This would be correct if the question was 'How far did the ball fall during the whole time of its flight?'. You just have to subtract the answer in C from this.
     
  16. Oct 24, 2006 #15
    Nice, thanks :).
     
  17. Oct 24, 2006 #16
    Time for class now, I'll post more questions if i need help later.
     
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