# Non elastic collision?

I am new here and still learning Mathematica in order to make use of it in my studies (physics). I am encountering one "issue". I wish to include non - elastic collision in simulation below: When particle's path intercepts condenser's plate, it should behave like in non elastic collision(dotted line should be "stopped" as in picture. In attachment are my code, current simulation and wanted output. Any help in what I should do and add in code will be highly appreciated! :) P.S. Here's the code:

Manipulate[
Grid[{{
Show[
Graphics[{
Text[Style["+", Large], {25, d/2}],
Text[Style["-", Large], {25, -d/2}],
Arrow[{{-2, 0}, {0, 0}}],
Line[{{0, d/2}, {22, d /2}}],
Line[{{0, -d /2}, {22, -d /2}}]
}],
d1 = d;
ParametricPlot[{v*t*Cos[a],
Piecewise[{
{0, t < 0},
{If[
c == "-", (v*t*Sin[a]) + U q/(2 d m) (t)^2, (v*t*Sin[a]) -
U q/(2 d m)*(t )^2], t > 0}}]}, {t,
0, (v^2*Sin[2*a]/ (U q/(d m )))},
PlotStyle -> {Red, Dashing[Small]}
],
Axes -> {True, True},
AxesOrigin -> {0, 0},
PlotRange -> {{-25, 25}, {-d/2, d/2}},
AspectRatio -> 0.5,
ImageSize -> 1.3 {400, 200}]},
{Text@Grid[{
{"Jačina el. polja " , "=", NumberForm[N[ U / d], {4, 2}] ,
"V/m" },
{"Domet " , "=",
NumberForm[N[ v^2*Sin[2*a]/ (U q/(d m ))], {4, 2}], "m"}},
Alignment -> Right]
}}],
{{d, 2, "Širina kondenzatora (m)"}, 1, 5, Appearance -> {"Labeled"}},
{{U, 50, "Napon na kondenzatoru (V)"}, 10, 100,
Appearance -> "Labeled"},
{{v, 5, "Početna brzina čestice (m/s)"}, 1, 10,
Appearance -> "Labeled"},
{{m, .5, "Masa čestice (kg)"}, .1, 1, Appearance -> "Labeled"},
{{q, 5, "Naelektrisanje čestice (C)"}, 1, 10,
Appearance -> "Labeled"},
{{a, Pi/3, "Upadni ugao"}, 0, 6.28, Appearance -> "Labeled"},
{{c, "+", "Znak naelektrisanja"}, {"+", "-"}}, ControlPlacement -> Top
] ]1[ ]2 • Welcome. You should post code instead of screenshot of code. By non-elastic (= not a perfect rebound), you mean inelastic (= absolutely no rebound), right? – anderstood Jan 16 '18 at 23:24
• Welcome to Mathematica.SE! I suggest the following: 1) As you receive help, try to give it too, by answering questions in your area of expertise. 2) Take the tour! 3) When you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. Also, please remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign! – Michael E2 Jan 17 '18 at 0:34
• Thank you @anderstood, I have added a real code. By that I do mean inelastic. Particle should have absolutely no rebound. – Vratovi Zvezda Jan 17 '18 at 8:50
• @anderstood ........ – Vratovi Zvezda Jan 17 '18 at 15:49
• If I follow correctly you mean this boundary is "absorbing". – Daniel Lichtblau Jan 17 '18 at 16:24

Strictly speaking, this is not an answer to you question. But, since you are studying physics, you might consider using NDSolve for this work. The code below describes the trajectory of an object moving inside a chamber, under the influence of it's initial conditions and gravity, with a lossy reflection each time it hits a wall.

eqs = {
x''[t] == 0, y''[t] == -2.1, x' == 1, y' == 5, x == 0,
y == .5,
WhenEvent[x[t] < 0 || x[t] > 1, x'[t] -> -.8 x'[t]],
WhenEvent[y[t] < 0 || y[t] > 1, y'[t] -> -.8 y'[t]]};

sol = NDSolveValue[eqs, {x[t], y[t]}, {t, 0, 10}];

ParametricPlot[sol, {t, 0, 10}, Prolog -> Rectangle[{0, 0}, {1, 1}]] • WhenEvent works as long as the "coefficient of restitution" (in your code, 0.8) is $>0$. If you set it at 0 as required by the OP, the event will be triggered at each time step and the constraint might be violated. – anderstood Jan 18 '18 at 22:10
Manipulate[
Grid[{{Show[
Graphics[{Text[Style["+", Large], {25, d/2}],
Text[Style["-", Large], {25, -d/2}], Arrow[{{-2, 0}, {0, 0}}],
Line[{{0, d/2}, {22, d/2}}], Line[{{0, -d/2}, {22, -d/2}}]}],

Module[{t1, t2},
t1 = t2 /.
Solve[{(v*t2*Sin[a]) - U q/(2 d m)*(t2)^2 == 0, t2 > 0}, t2];
If[t1 === {}, t1 = Infinity, t1 = First[Sort@t1]];
ParametricPlot[{Piecewise[{{v*t*Cos[a], t < t1/2}, {t,
t > t1}}],
Piecewise[{{0,
t < 0}, {If[
c == "-", (v*t*Sin[a]) + U q/(2 d m) (t)^2, (v*t*Sin[a]) -
U q/(2 d m)*(t)^2], 0 < t < t1}, {d/2,
t >= t1/2}}]}, {t, 0, (2 v^2*Sin[2*a]/(U q/(d m)))},
PlotStyle -> {Red, Dashing[Small]}]], Axes -> {True, True},
AxesOrigin -> {0, 0}, PlotRange -> {{-25, 25}, {-d/2, d/2}},
AspectRatio -> 0.5, ImageSize -> 1.3 {400, 200}]}, {Text@
Grid[{{"Jačina el. polja ", "=", NumberForm[N[U/d], {4, 2}],
"V/m"}, {"Domet ", "=",
NumberForm[N[v^2*Sin[2*a]/(U q/(d m))], {4, 2}], "m"}},
Alignment -> Right]}}],
{{d, 5., "Širina kondenzatora (m)"}, 1, 5,
Appearance -> {"Labeled"}}, {{U, 10., "Napon na kondenzatoru (V)"},
10, 100, Appearance -> "Labeled"}, {{v, 9.5,
"Početna brzina čestice (m/s)"}, 1, 10,
Appearance -> "Labeled"}, {{m, .95, "Masa čestice (kg)"}, .1, 1,
Appearance -> "Labeled"}, {{q, 5, "Naelektrisanje čestice (C)"}, 1,
10, Appearance -> "Labeled"}, {{a, Pi/3, "Upadni ugao"}, 0, 6.28,
Appearance -> "Labeled"}, {{c, "+", "Znak naelektrisanja"}, {"+",
"-"}}, ControlPlacement -> Top] • Thank you very much. This answers my questin but only if there is a "collision with a plate. In other cases I receive something like in the last picture. – Vratovi Zvezda Jan 18 '18 at 21:23