Re: A problem with Manipulate

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• Subject: [mg127903] Re: A problem with Manipulate
• From: Dominik Hezel <sendme2000 at me.com>
• Date: Fri, 31 Aug 2012 03:57:45 -0400 (EDT)
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• References: <k1ch1e\$n2t\$1@smc.vnet.net>

```On Sunday, August 26, 2012 8:51:26 AM UTC+2, Sergio Miguel Terrazas Porras wrote:
> Hello guys, I am having a problem with a Manipulate I wrote, to ilustrate a physics problem.
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> 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).
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> 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.
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> I will appreciate any help, as I am frustrated at not beeig able to fix the problem.
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> Thanks
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> d;H=10;r01={0,0};\[Theta]=ArcTan[H/d];a=9.8*{0,-1};
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> r02={d,H};
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> chango
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> chango:=Manipulate[Module[{v0,r1,r2,linea,flecha,chango},
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> v0=vi*{Cos[\[Theta]],Sin[\[Theta]]};
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> r1[t_]=r01+v0*t+1/2 a*t^2;
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> r2[t_]=r02+1/2 a*t^2;
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> linea=Graphics[{Red,Dashing[{.01,.01}],Line[{r01,r02}]}];
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> flecha=Graphics[Arrow[{r01,r2[t]}]];
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> trayectoria1=ParametricPlot[r1[z],{z,0,t+.001}];
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> trayectoria2=ParametricPlot[r2[z],{z,0,t+.001},PlotStyle->{Dashing[.02],Brown}];
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> chango=Graphics[{Brown,PointSize[.03],Point[r2[t]]}];
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> (*Time of Flight*)
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> tf=Dynamic[H/(vi*Sin[\[Theta]])];
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> Show[flecha,chango,linea,trayectoria1,trayectoria2,PlotRange->All]
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> ]
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> ,{{vi,10,"Subscript[v, i]"},{10,15,20}},{{t,0},0,tf,Appearance->"Labeled"},TrackedSymbols->{vi,t,tf},SaveDefinitions->True]

Some of the code is opaque to me, but if you define 'd' at the very beginning, at least something happens and it's not all red.

```

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