2008-07

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Projectile with Air Resistance (Fdrag = -bv)

Clear["Global`*"];

eqm = {m v'[t] == -m g - b v[t], y'[t] == v[t]};

init = {y[0] == y0, y'[0] == v0};

dsol = DSolve[Join[eqm, init], {v, y}, t] // Flatten // Simplify;
{v[t], y[t]} /. dsol

vterm = v[t] /. dsol /. {t -> large m/b} // ExpandAll

vterm = Limit [vterm, large -> Infinity]

{ynar[t], vnar[t]} = Limit[{y[t], v[t]} /. dsol, b -> 0]

val1 = {g -> 9.8, m -> 1, y0 -> 0, v0 -> 0};

coord1[b_] = {t, y[t]} /. dsol /. val1 // Simplify

coord1[0] = {t, ynar[t]} /. val1

Clear[plot1];
plot1[b_] := ParametricPlot[Evaluate[coord1[b], {t, 0, 10}]]; plotarray1 =
Table[plot1[b], {b, 0, 1, 1/2}];

Show[plotarray1,
Graphics[{Text["b=0", {5, -200}], Text["b=1/2", {8, -150}],
Text["b=1", {9, -50}]}], Frame -> True,
FrameLabel -> {"t", "y", "Effect of Air Resistance", ""}];

coord2[b_] = {t, v[t]} /. dsol /. val1 // ExpandAll
coord2[0] = {t, vnar[t]} /. val1;

coord3[b_] = {t, vterm} /. dsol /. val1 // ExpandAll
coord3[0] = {t, 0};

Clear[plot2];
plot2[b_] := ParametricPlot[Evaluate[{coord2[b], coord3[b]}], {t, 0, 10}]
plotarray2 = Table[plot2[b], {b, 0, 1, 1/2}];

Show[plotarray2,
Graphics[{Text["b=0", {3.5, -25}], Text["b=1/2", {7, -17}],
Text["b=1", {8, -7}]}], PlotRange -> {0, -30}, Frame -> True,
RotateLabel -> False,
FrameLabel -> {"t", "v", "Effect of Air Resistance", ""}];

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http://letsphysics.blog17.fc2.com/tb.php/225-6fc5264f

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