# Parametric plot / I just need to check my work (quick)

$$x(t)= \left( u\cos A \right) t$$

and

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

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

$$u = 125 \mbox{ ft/s}$$

$$g = 32 \mbox{ ft/s}^2$$

$$h = 3 \mbox{ ft}$$

$$A$$ may take several different values. Here follows the random choices I made and the corresponding graphs:

$$A=\frac{\pi}{3}$$

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

$$A=\frac{4\pi}{9}$$

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

$$A=\frac{\pi}{2}$$

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:

NateTG
Homework Helper
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.)

NateTG said:
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.)

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.

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.

Oh, no!!! That's a typo. u = 125 ft/s. The units are incorrect in my 1st post.

whozum said: