graph won't plot in correct spot

% plot mountain
Mn_x = [0, 1000, 3014.8];
Mn_y = [0, 6, 1000];
plot (Mn_x, Mn_y)
hold on
% known variables
Xo = 0;
Yo = 1;
V = 585; % m/s
G = 9.81; % m/s^2
t = linspace(0, 8, 800);
th1 = 10; % degrees
th2 = 12; % degrees
th3 = 14; % degrees
% calculate trajectory of howitzer
x_th1 = Xo + (V * cos(th1)) * t
y_th1 = Yo + (V * sin(th1)) * t - 1/2 * G * (t.^2)
plot (x_th1, y_th1, 'r') 

Plot (x_th1, y_th1) is supposed to start at (0,1) but actually starts at (-3900,-2800) I've tried fixing the equations but I can't figure out whats wrong.

Answer 1

[Walter Roberson]

If you do not want negative values shown, then clip them out of the plot by adjusting xlim and ylim.

% plot mountain
Mn_x = [0, 1000, 3014.8];
Mn_y = [0, 6, 1000];
plot (Mn_x, Mn_y)
hold on
% known variables
Xo = 0;
Yo = 1;
V = 585; % m/s
G = 9.81; % m/s^2
t = linspace(0, 8, 800);
th1 = 10; % degrees
th2 = 12; % degrees
th3 = 14; % degrees
% calculate trajectory of howitzer
x_th1 = Xo + (V * cos(th1)) * t

x_th1 = 1×800

0 -4.9147 -9.8294 -14.7441 -19.6588 -24.5736 -29.4883 -34.4030 -39.3177 -44.2324 -49.1471 -54.0618 -58.9765 -63.8913 -68.8060 -73.7207 -78.6354 -83.5501 -88.4648 -93.3795 -98.2942 -103.2089 -108.1237 -113.0384 -117.9531 -122.8678 -127.7825 -132.6972 -137.6119 -142.5266

y_th1 = Yo + (V * sin(th1)) * t - 1/2 * G * (t.^2)

y_th1 = 1×800

1.0000 -2.1870 -5.3750 -8.5639 -11.7539 -14.9448 -18.1367 -21.3296 -24.5235 -27.7184 -30.9142 -34.1111 -37.3089 -40.5077 -43.7075 -46.9082 -50.1100 -53.3127 -56.5164 -59.7211 -62.9268 -66.1335 -69.3411 -72.5498 -75.7594 -78.9700 -82.1816 -85.3941 -88.6077 -91.8222

plot (x_th1, y_th1, 'r') 

XL = xlim();
YL = ylim();
xlim( [max(0, XL(1)), XL(2)]);
ylim( [max(1, YL(1)), YL(2)]);

[Walter Roberson]

Reminder: cos() and sin() expect radians . If you want to work with degrees, you need cosd() and sind()