Projectile motion without drag

I've been trying to figure out how to make this script work for matlabs, but am getting a return that says "Index exceeds the number of array elements (1).. ..x(k+1)=Vx(k)*delt;" if anymore explantion if needed let me know (script below). Thank you!

%Projectile motion with and without drag
%Constants
gc=32.174;
g=-32.174;
v0=100;
ang=30;
ang=ang*pi/180;
mass=0.4;
weight=0.4;
area=11.34;
cd=0.6;
delt=0.1;
x0=0;
y0=0;

%Projectile motion without drag
x(1)=0;
y(1)=0;
Vx=v0*cos(ang);
Vy=v0*sin(ang);
k=1;

while y(k)>=0
    Vy(k+1)=Vy(k)+g*delt;
    
    y(k+1)=Vy(k)*delt;
    x(k+1)=Vx(k)*delt;
    k=k+1;
end 
Xmax=max(x)
Ymax=max(y)

%with Drag%

Answer 1

[James Tursa]

You don't define the Vx(k) value before using it, hence the error. Since your Vx values don't change you can fix this error by simply removing the indexing for it. Or you could add a line to define Vx(k) for each k step.

Also, you need to add the velocity*dt to the current position. What you are doing is simply assigning the velocity*dt to the position.

So the code changes would be:

    Vx(k+1) = Vx(k);
    y(k+1) = y(k) + Vy(k)*delt;
    x(k+1) = x(k) + Vx(k)*delt;

Adding the code to assign Vx(k+1) will make the code easier to modify once you add drag, because Vx(k+1) will in fact be changing from step to step in that case.

As an aside, I would advise annotating all of your numbers with unit comments. This makes your code much more readable and easier to spot unit errors. E.g.,

gc=32.174; % (m/s^2)
g=-32.174; % (m/s^2)
v0=100; % (m/s)
ang=30; % (deg)
etc.

[DiamondsRain]

Thank you much this helped a lot!