# How to plot derivative vectors on a parabolic trajectory?

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Alexander Hellberg on 15 Mar 2021
Answered: Shubham Rawat on 22 Mar 2021
Greetings
I have to plot a symple parabolic trajectory with the derivative vectors in different point. So far I have:
v = 20;
g = -9.81;
h = 50;
a = (1/2) * g;
b = v;
c = h;
tFinal = roots([a, b, c]);
t = [0:0.1:120];
x = v*t;
y = h + v*t + g*t.^2*(1/2);
dx = v;
dy= v +g*t;
plot(x, y)
axis([0 120 0 75])
hold on;
How can I add the velocity vectors for discrete (not important where) values of the trajectory?
Thank you so much!

Shubham Rawat on 22 Mar 2021
Hi Alexander,
You may look at this code. I have created tangents at some points of the curve.
%at these point of time creating tangents
t2 = [0:1:120];
%determining slopes at each time frame
slope = (v+g*t2)/v;
delx = 7; %delta x
%points of tangents at each t2
x2 = v*t2;
x22 = x2 + delx;
y2 = h + v*t2 + g*t2.^2*(1/2);
y22 = y2 + slope*delx;
%plotting the tangent
plot([x2;x22], [y2;y22], 'Color', 'r');
Hope this Helps!