Help with plotting projectile motion with a for loop

Hey guys,

I've been working on this script for the past two days and I've hit a wall. What needs to happen, is the user inputs various data then it spits out a graph with the projectile trajectory. I'm very new to any kind of coding, and any and all help is appreciated.

Here's the code:

close all; clear all; clc;
theta1 = input('What is the desired launch angle in degrees? ' );
theta = rad2deg(theta1);
x0 = input('What is the initial horizonal position in meters? ');
y0 = input('What is the initial vertical position in meters? ');
v0 = input('What is the initial launch velocity in m/sec? ');
%m = input('What is the mass of the object in kg? ');
g = -input('What is the desired acceleration due to gravity? ');
xmax = ((v0.^2).*sin(2.*(theta)./g));
ymax = ((v0.^2).*(sin(theta).^2))./g;
time1 = ((2.*v0.*sin(theta))./g);
time2 = ['Amount of time in flight: ', num2str(time1)];
xmax1 = ['Distance the object traveled: ', num2str(xmax)];
ymax1 = ['Maximum height reached: ', num2str(ymax)];
t = 0 : .01 :500;
angles = length(theta);
for k = 1 : angles;
  %angle = theta(k);
  xvelo = v0 * cos(theta);
  yvelo = v0 * sin(theta);
  x = xvelo .* t + (1/2) * x0 .* t.^2;
  y = yvelo .* t + (1/2) * g .* t.^2;
  plot(x, y, 'Linewidth', 1.5);
  grid on;  
end
disp(time2);
disp(xmax1);
disp(ymax1);
disp(theta);

Answer 1

[Walter Roberson]

theta = rad2deg(theta1);

is the wrong way around: your prompt is in degrees, so if you are going to convert at all it should be deg2rad() . If you decide to leave it in degrees then use sind() and cosd() instead of sin() and cos()

[James Finch]

Thank you! That's definitely helpful. I'm having a hard time with the loop working correctly as well.

[Walter Roberson]

The wording of your prompt implies that the user is expected to input a single degree angle, but your loop is over the number of degree angles input. If you are expecting the user to input multiple angles then you should change the prompt.

If the user does input multiple angles, then do you want all of the trajectories to appear on the same graph? If so then you will need to add a

hold on

after the first plot()