displays nothing when I plot Please help

Hello all,

I have tried numerous different methods to get this to plot. It still does nothing. Please help...

If you are feeling super nice I would like it to plot x from 0 to 13

y_o = 0;
x_o = 0;

dt=.001;
t = 0:dt:1.1;
g = -32.2;

a = 45


x_t = 4
x (1) = x_o;
y(1) = y_o;

syms v t 
eqn3 = v > 0;
eqn4 = t > 0;
eqn1 = x_t ==  v  * cosd (a) *t;
eqn2 = t  == (2 * v * sind(a))/g ;
eqns =[eqn1,eqn2];

sol = solve([eqns],[v,t]);
vS = vpa(sol.v)/1i;    
tS = vpa(sol.t)/1i;

sol = solve([eqn3,eqn4],[v,t]);
vpos = vS(vS>=0);
tpos = tS(tS>=0);

vpos
tpos
dt=.01;
t_i = 0:dt:tpos;

y  = zeros(1,length(tpos));
x = zeros(1,length(tpos));
vy = zeros(1,length(tpos));

Simulate the trajectory

vy = vpa(vpos * sind(a));


for i = 2 :length(tpos)
    vy (i) = vy(i-1) + g * dt;
    x (i) = x (i-1) + vpos * cosd(a) * dt;
    y (i) = y(i-1) + vy(i) * dt + 1/2 * g * dt.^2;
    

end
vy 
x
y

ymax= vpa(1/2 * vpos * sind(a)* tpos)

Plotting the balls path

    plot (x,y)
title Projectile Motion

Answer 1

[Walter Roberson]

y_o = 0;
x_o = 0;

dt=.001;
t = 0:dt:1.1;    %NOT USED, WHY DOES THIS EXIST?
g = -32.2;

a = 45;


x_t = 4;
x (1) = x_o;
y(1) = y_o;

syms v t 
eqn3 = v > 0;
eqn4 = t > 0;
eqn1 = x_t ==  v  * cosd (a) *t;
eqn2 = t  == (2 * v * sind(a))/g ;
eqns =[eqn1,eqn2];

sol = solve([eqns],[v,t]);
vS = vpa(sol.v)/1i;    
tS = vpa(sol.t)/1i;

sol = solve([eqn3,eqn4],[v,t]);
vpos = vS(vS>=0);
tpos = tS(tS>=0);

vpos

vpos = 

11.349008767288886009586274243886

tpos

tpos = 

0.49844478627922681821464009813854

dt=.01;
t_i = 0:dt:tpos;
numt = length(t_i);
y  = zeros(1,numt);
x = zeros(1,numt);
vy = zeros(1,numt);

vy(1) = vpa(vpos * sind(a));


for i = 2 :numt
    vy (i) = vy(i-1) + g * dt;
    x (i) = x(i-1) + vpos * cosd(a) * dt;
    y (i) = y(i-1) + vy(i) * dt + 1/2 * g * dt.^2;
    

end
vy 

vy = 1×50

8.0250 7.7030 7.3810 7.0590 6.7370 6.4150 6.0930 5.7710 5.4490 5.1270 4.8050 4.4830 4.1610 3.8390 3.5170 3.1950 2.8730 2.5510 2.2290 1.9070 1.5850 1.2630 0.9410 0.6190 0.2970 -0.0250 -0.3470 -0.6690 -0.9910 -1.3130

x

x = 1×50

0 0.0802 0.1605 0.2407 0.3210 0.4012 0.4815 0.5617 0.6420 0.7222 0.8025 0.8827 0.9630 1.0432 1.1235 1.2037 1.2840 1.3642 1.4445 1.5247 1.6050 1.6852 1.7655 1.8457 1.9260 2.0062 2.0865 2.1667 2.2470 2.3272

y

y = 1×50

0 0.0754 0.1476 0.2166 0.2824 0.3449 0.4042 0.4603 0.5132 0.5629 0.6093 0.6525 0.6925 0.7293 0.7629 0.7932 0.8203 0.8442 0.8649 0.8824 0.8966 0.9076 0.9154 0.9200 0.9214 0.9195 0.9144 0.9061 0.8946 0.8798

ymax= vpa(1/2 * vpos * sind(a)* tpos)

ymax = 

2.0

    plot (x,y)
title Projectile Motion

[Susan Chestnutt]

Thank you!! You're wonderful!!!!