Projectile Motion 2D plot without drag

Hi all. I am plotting a 2D plot of projectile motion, where speed and height are on the y axis and time is on the x axis. My speed is wrong, however. The speed is correct when plotted by itself, but when plotted with height, the graph seems to shift to the left. The point at which speed is supposed to be 0 is at t = 3.0581 s, which is what happens when I plot it on its own. But in the plot below its at 2.7 or 2.8 seconds. How do I fix this? I'm pretty sure there's something wrong with my 2D plot specification but I'm not sure what.

function [v, h] = projectile (v_0, theta, diagram)
% Gravitational acceleration, in m/s^2
g = 9.81;
% Time taken to hit the ground, s
t_hit = 2*(v_0/g)*sind(theta);
% Overall time taken from launch to hitting ground, s
t = 0:0.005:t_hit;
% Height, m
h = v_0*t*sind(theta)-(1/2)*g*(t.^2);
% Speed, m/s
v = sqrt(((v_0)^2)-(2*v_0*g*t*sind(theta))+(g^2)*(t.^2));

      % Optional plotting; diagram = 1 is a true condition so v, h and plots
      % will be outputted, otherwise diagram = 0 is a false condition and 
      % only v and h are outputted
      if diagram == 1;
          [ax,p1,p2] = plotyy(t,h,t,v);
          set(p1,'linewidth',1.5);
          set(p2,'linewidth',1.5);
          % Label x-axis
          xlabel(ax(1),'Time (s)')
          % Label left y-axis
          ylabel(ax(1),'Height (m)')
          % Label right y-axis
          ylabel(ax(2),'Speed (m/s)')
          % Set limits for x-axis
          set(ax(1),'XLim',[0 6.1162]);
          set(ax(1),'XTick',[0:1:6.1162]);
          % Set limits for left y-axis
          set(ax(1),'YLim',[0 45.8550]);
          set(ax(1),'YTick',[0:20:45.8550]);
          % Set limits for right y-axis
          set(ax(2),'YLim',[0 30]);
          set(ax(2),'YTick',[0:10:30]);
          % Vertical grid lines only
          set(gca,'XGrid','on')
          set(gca,'YGrid','off')
      else
          diagram = 0;
      end
  end

[Image Analyst]

How did you call it? What did you pass in for v_0, theta, & diagram?

[MG]

I call

projectile(30, 90, 1)

if I want to plot. The diagram option is supposed to be there.

Answer 1

[Image Analyst]

Get rid of your messed up xlim, ylim, xtick, and ytick calls and it looks fine:

[MG]

That's not how its supposed to look, though. Its supposed to look like this.

Also, I hope you saw the previous edit in my comment. I meant projectile(30, 90, 1) not projectile(20, 90, 1), sorry.

[Image Analyst]

I just assumed your formulas were correct. They're probably not. Recheck them. Compare against the formula here: https://en.wikipedia.org/wiki/Projectile_motion#Velocity

[MG]

I checked them and they are correct. I copied them from the assignment file and they also match what it says in wiki. I don't think there's anything wrong with the equations, there's something wrong with the graph. Because if I plot v and h separately, everything is correct.

[Image Analyst]

You altered the x axis for the first curve but not the second. So either put in this line:

set(ax(2),'XLim',[0 6.1162]);

or take out this line:

set(ax(1),'XLim',[0 6.1162]);

[MG]

That did the trick, thank you!!