# How to create matrix array using while loop and time increment?

34 views (last 30 days)
Kenny Gee on 16 Feb 2022
Commented: Kenny Gee on 16 Feb 2022
I have a problem where i want to solve a problem where an apple falls from a tree from 3m before hitting the ground. Assuming there is no air resistance, how long will it take to hit the ground? I have to create an array with time increments until the distance becomes 0 at the final time. So first column should show my time and second column will show the distance going down at every increment.
y0=2;
g=-9.81;
t = 0;
i=0;
y1=y0;
a = zeros([],2);
while y1>=0
i=i+1;
t=t+0.10;
y1=y0-0.5*g*t.^2;
a(i,:) = [t,y1]
end
disp(a)
0.0065 2.0726 %sample results
0.0065 2.0789
0.0065 2.0853
0.0065 2.0917
0.0065 2.0981
0.0066 2.1046
0.0066 2.1110
0.0066 2.1174
But when I run my code, it won't stop running and instead of 0.10 increments, the time looks off. How do I use the while loop (must use) to find the time it takes for the final y value to be 0.

DGM on 16 Feb 2022
Edited: DGM on 16 Feb 2022
Well, that's what happens when you drop an anti-gravity apple.
y0 = 2;
g = -9.81;
tstep = 0.01;
t = 0;
i = 0;
y1 = y0;
a = zeros([],2);
while y1 >= 0
i = i + 1;
t = t + tstep;
y1 = y0 + 0.5*g*t.^2;
a(i,:) = [t,y1];
end
plot(a(:,1),a(:,2))
Kenny Gee on 16 Feb 2022
okay, i see where i made my mistake. sorry about the actual equation. I wanted to learn to do while loop. Thank you :)

David Hill on 16 Feb 2022
y1=y0+0.5*g*t.^2;%needs to be + (gravity is negative)
Kenny Gee on 16 Feb 2022
yes you are right. Thank you

### Categories

Find more on Loops and Conditional Statements in Help Center and File Exchange

R2021b

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by