A problem with Manipulate

• To: mathgroup at smc.vnet.net
• Subject: [mg127843] A problem with Manipulate
• From: Sergio Miguel Terrazas Porras <sterraza at uacj.mx>
• Date: Sun, 26 Aug 2012 02:51:43 -0400 (EDT)
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```Hello guys, I am having a problem with a Manipulate I wrote, to ilustrate a physics problem.

If you aim at an object that is hanging a height H at a distance D. And at the instant you shoot, the object starts to fall, you will alwais hit it, regardless os the initial speed (provided the floor does not interfere).

However, if I make an evaluation, it works fine, but when I change the speed, it "remembers" the time of flight of the preceding speed.

I will appreciate any help, as I am frustrated at not beeig able to fix the problem.

Thanks

d;H=10;r01={0,0};\[Theta]=ArcTan[H/d];a=9.8*{0,-1};
r02={d,H};
chango
chango:=Manipulate[Module[{v0,r1,r2,linea,flecha,chango},
v0=vi*{Cos[\[Theta]],Sin[\[Theta]]};
r1[t_]=r01+v0*t+1/2 a*t^2;
r2[t_]=r02+1/2 a*t^2;

linea=Graphics[{Red,Dashing[{.01,.01}],Line[{r01,r02}]}];

flecha=Graphics[Arrow[{r01,r2[t]}]];

trayectoria1=ParametricPlot[r1[z],{z,0,t+.001}];

trayectoria2=ParametricPlot[r2[z],{z,0,t+.001},PlotStyle->{Dashing[.02],Brown}];

chango=Graphics[{Brown,PointSize[.03],Point[r2[t]]}];

(*Time of Flight*)
tf=Dynamic[H/(vi*Sin[\[Theta]])];

Show[flecha,chango,linea,trayectoria1,trayectoria2,PlotRange->All]
]
,{{vi,10,"Subscript[v, i]"},{10,15,20}},{{t,0},0,tf,Appearance->"Labeled"},TrackedSymbols->{vi,t,tf},SaveDefinitions->True]

```

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