Re: newbie here,, need help with parametrics

*To*: mathgroup at smc.vnet.net*Subject*: [mg96525] Re: [mg96455] newbie here,, need help with parametrics*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Mon, 16 Feb 2009 06:52:32 -0500 (EST)*References*: <200902140807.DAA17042@smc.vnet.net>*Reply-to*: drmajorbob at longhorns.com

Load AccelerationDueToGravity from the PhysicalConstants package, and Convert from the Units package: Needs["PhysicalConstants`"] Needs["Units`"] Calculate g in ft/sec^2 (with units removed): g = Convert[AccelerationDueToGravity, Foot/Second^2]/(Foot/Second^2) 196133/6096 (AccelerationDueToGravity is in meters/sec^2.) Define the {x, y} coordinates at time t: r[a_, x_, y_, v_][t_] = {x + t v Cos@a, y + t v Sin@a - 1/2 g t^2} {x + t v Cos[a], -((196133 t^2)/12192) + y + t v Sin[a]} Plot the curve: ParametricPlot[r[30. Degree, 0, 32, 32][t], {t, 0, 2}, PlotRange -> All] Here's a general solution for y == 0: Solve[0 == Last@r[a, x, y, v][t], {t}] {{t -> (4 (1524 v Sin[a] - Sqrt[762] Sqrt[196133 y + 3048 v^2 Sin[a]^2]))/196133}, {t -> ( 4 (1524 v Sin[a] + Sqrt[762] Sqrt[196133 y + 3048 v^2 Sin[a]^2]))/ 196133}} The second solution is the one you need, as the example shows: Solve[0 == Last@r[30. Degree, 0, 32, 32][t], {t}] tDrop = t /. Last@% {{t -> -0.998192}, {t -> 1.99278}} 1.99278 How far did the projectile travel horizontally? r[30. Degree, 0, 32, 32][tDrop] {55.2256, 0.} About 55 feet. Bobby On Sat, 14 Feb 2009 02:07:05 -0600, R.J. <nemocamaro at epix.net> wrote: > I am using Mathematica and i'd rather be using derive,,,,, but > anyways,, heres the problem i have to do, a baseball is thrown from the > stands 32 feet from the ground at an angle of 30 degrees above the > horizontal, initial velocity is 32 feet per second. > > what i want to do is find how to plot this in mathematica,, the graph i > keep getting says it hits the ground after .8 seconds, and i know > thats not right,,, here is the formula i am using > > r = (x + v Cos a) t) i + (y + (v Sin a) t - 1/2 gt^2) j > > where x is the initial x position and y is the initial height, v is the > initial velocity a is the angle (30*) t is time and g is the > gravitational constant.. > > i'm stuck,,, any help? > -- DrMajorBob at longhorns.com

**References**:**newbie here,, need help with parametrics***From:*"R.J." <nemocamaro@epix.net>