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Homework Help: Parametric plot / I just need to check my work (quick)

  1. Jun 10, 2005 #1
    [tex]x(t)= \left( u\cos A \right) t[/tex]

    and

    [tex]y(t)= \left( u\sin A \right) t - \frac{gt^2}{2} + h[/tex]

    represent the horizontal and vertical coordinates of a batted or thrown baseball. [tex]A[/tex] is the initial angle of elevation and [tex]u[/tex] is the initial speed of the ball. I need to plot [tex]x(t)[/tex] and [tex]y(t)[/tex] parametrically. I'm given the following

    [tex]u = 125 \mbox{ ft/s}[/tex]

    [tex]g = 32 \mbox{ ft/s}^2[/tex]

    [tex]h = 3 \mbox{ ft}[/tex]

    [tex]A[/tex] may take several different values. Here follows the random choices I made and the corresponding graphs:

    [tex]A=\frac{\pi}{3}[/tex]

    http://img25.imagevenue.com/img.php?loc=loc93ℑ=663_parametricplot_1.jpg

    [tex]A=\frac{4\pi}{9}[/tex]

    http://img6.imagevenue.com/img.php?loc=loc123ℑ=26c_parametricplot_2.jpg

    [tex]A=\frac{\pi}{2}[/tex]

    http://img6.imagevenue.com/img.php?loc=loc123ℑ=26c_parametricplot_2.jpg

    Could you please take a quick look at those graphs? In my opinion, there seems to be something wrong.

    Thank you
     
    Last edited: Jun 10, 2005
  2. jcsd
  3. Jun 10, 2005 #2

    NateTG

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    I can't see the images. You should be getting parabolas for the first two, and a vertical line for the third (since the ball goes straight up and down.)
     
  4. Jun 10, 2005 #3
    Oh, I'm sorry about that. I actually tested the links, but a minute later they just wouldn't work. If you still wanna take a quick look, I placed them at:

    photos.yahoo.com/thiago_j

    They're the only ones there. What you said about the shapes sound right to me, but that's not what I have. They are pretty much the same. I used the command (mathematica 5):

    ParametricPlot[{x(t), y(t)}, {t, t_min, t_max}]

    Anyway, that's definitely stange.
     
  5. Jun 10, 2005 #4
    The discrepancy is probably because you cite g in feet per second squared and your initial velocity in meters per second. Your equation forms are correct.
     
  6. Jun 10, 2005 #5
    Oh, no!!! That's a typo. u = 125 ft/s. The units are incorrect in my 1st post.
     
  7. Jun 10, 2005 #6
    I don't have a clue what else I could do.
     
  8. Jun 10, 2005 #7
    I managed to get in my calculator what NateTG predicted: "getting parabolas for the first two, and a vertical line for the third". All I gotta do now is go over my mathematica command so that I can fix it.

    Thank you guys
     
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