Script for solving Newton’s laws of motion & plotting an object's trajectory

Hello,

I am very much new to Matlab and coming from C++. I need help in how to the script would look for the following equation and then plotting the results:

Xt = cos(A*pi/180) * V0 * T
Yt = sin(A*pi/180) * V0 * T - 0.5*g*T^2

I'm trying to write a MATLAB program consisting of the function

function PlotTrajectory(V0, A, TimeStop, StepValue)

Do I initialize the values of A(angle in degrees), V0(initial velocity), g, T (time at position of the object)?

Answer 1

[Zoltán Csáti]

Write it into the Editor:

A = 10;
v0 = 2;
T = 5;
t = 0:0.01:T;
g = 9.81;
x = cos(A*pi/180)*v0*t;
y = sin(A*pi/180)*v0*t - 0.5*g*t.^2;
plot(t,x,t,y);

[Kyle]

Thank you!

One more question, what if I wanted to plot various times, angles & initial velocities rather than have A always = 10, V0 = 2 & T = 5?

For example, PlotTrajectory(88.0, 42.0, 5.0, 0.1);

Answer 2

[Star Strider]

It’s not necesary to initialise them in your function, since all variables are local to the function. It is always a good idea to preallocate vectors and matrices, especially if they are supposed to have specific sizes (for instance a row or column vector) as output, and for speed.

It is always advisable to vectorise your equations to allow for element-by-element operations, since the default behaviour in MATLAB is to use array operations:

Xt = cos(A*pi/180) * V0 * T;
Yt = sin(A*pi/180) * V0 * T - 0.5*g*T.^2;

I vectorised the ‘T.^2’ operation here (with (.^) replacing (^)), anticipating that ‘T’ will be a vector.

The semicolons at the end of the statements suppress the default behaviour of printing the value of that variable to the Command Window.

Answer 3

[Zoltán Csáti]

As Star Strider said, create a function to pass those arguments.