(Same trajectory problem now with different plot results and problems). I'm trying to write a script that will plot a balls trajectory.

Intial position and velocity are known (Vi, xi, yi), and air resistance is neglected. Originally I used t=zeros(1,3600); and with the help of someone else t(k2)=(k2-1)*dt; where dt is defined as 1. In this iteration tried to get Y and YX to run 10 iterations from 0 seconds to 'tend', the time when the ball lands. I'm lost in the wind here so any help would be appreciated.

% %%%%code below is what I'm trying to run (still haven't figured out formatting for these message boards, code stops at 'plot(YX,Y)'%%%
%initial values
xi=0;
yi=0;
Vi= 20; % meters per second
g=-9.81; %meters per second squared
THy=[5:10:85];
THx=[0:1:90];
t=zeros(1,10);   

for k1 = 1:length(THy)
    for k2=1:10

          vyi=Vi.*sind(THy(k1));%initail vel. in y
          vyx=Vi.*cosd(THy(k1));%initial vel. in x 

          %t(k2)=(k2-1)*dt;
          %vyi=Vi.*sind(THy(k1));
          tvzero=vyi./g;%time when ball is at max height
          tend=2.*tvzero;%time when ball hits the ground
          dt=tend./10;
          t(k2)=(k2-1)*dt;

          %position of the ball     
          Y(k1,k2)=yi+vyi.*t(k2)+.5.*g.*(t(k2).^2);%height of the ball
          YX(k1,k2)=xi+vyx.*t(k2);%horizonatal distance traveled, no air resitance
      end
  end
  plot(YX,Y)

Answer 1

[Star Strider]

Two changes:

1. Make ‘g’ positive here:

g = 9.81; %meters per second squared

2. Switch the indices and subtract the gravitational acceleration term here:

Y(k2,k1)=yi+vyi.*t(k2)-0.5.*g.*(t(k2).^2);%height of the ball
YX(k2,k1)=xi+vyx.*t(k2);%horizonatal distance traveled, no air resitance

and you get the plot you want (or at least one that looks good to me).

[Jordan]

thank you much! I never would've thought to try that

[Star Strider]

My pleasure!

When I saw that ‘tvzero’ was negative, the ‘g’ problem revealed itself. Then experimenting with transposing the matrices gave the correct plot.