# Could someone perhaps guide me in the right direction to figure out a way to start this code?

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Collin Kerr on 21 Apr 2016
Commented: Collin Kerr on 28 Apr 2016
(Assignment) "Your program should also have a feature that predicts the velocities and elevation angles at which the projectile can be launched to hit a target given a specified distance. The input to this part of the program should be only the target distance. The output from this part of the program should be the velocities and launch angles for the projectile."
I don't see a way to get both those outputs by just inputting a distance. I'm not asking for someone to give me a code, but just a something to help me start.
Collin Kerr on 21 Apr 2016
clc,clear
F = input('Targeted Distance = ');
V_o = input('Velocity at launch = ');
Theta = input('Elevation angle at launch = ');
a=-9.81; %Its a given
b=V_o*sind(Theta) %It makes the coding a bit less confusing.
c=0; %Also a given
fprintf('The targeted distance for the launch is %d meters. \n', F)
fprintf('The velocity for the launch is %d meters per second. \n', V_o)
fprintf('The elevation angle for the launch is %d degrees. \n', Theta);
Q1=(-b-sqrt(b^2-4*a*c))/(a); %The 1/2 and times 2 cross out for the denom
disp(Q1)
%%Horizontal Range
H = V_o*cosd(Theta)*(Q1);
fprintf('The Horizontal Range of the launch is %0.3f \n', H)
%%Vertical Height
V = (b^2)/(a*2)*2;
fprintf('The Vertical Height of the launch is %0.3f \n', V)

Arnab Sen on 25 Apr 2016
Hi Collin,
In this case there would be multiple velocity and launch angles. The formulae for projectile distance is
d=(v^2/g). sin(2.theta).
where v is initial velocity, g gravitational acceleration and theta is projection angle.
Now if d is given, then relation between v and theta will be,
v=sqrt(d.g.cosec(2.theta)).
Now, you can vary the theta from 1 to 90 degree in specific interval (e.g. 1 degree)and get corresponding velocities v and out the angle and their corresponding velocities in a table format.
Collin Kerr on 28 Apr 2016
buttonNumber = menu ('Select the targeted distance','8','9','10','11','12','13','14','15');
T = buttonNumber + 7;
velocities = linspace(8, 15, 1000);
angles = linspace(10, 80, 1000);
[V, A] = meshgrid(velocities, angles);
distanceImage= (V^2./a)*sin(2.*velocities)
imshow(distanceImage, []);
hold on;
contour(V,A,distanceImage)