How EXACTLY doe the solve function work?

I'm trying to solve a simple projectile motion problem using the solve command, but it does not recognize already-assigned variables, and outputs an answer that is a function of itself. Am I misunderstanding how solve works? Apologizing in advanced for the bad formatting; I can't figure out how to work it.

if true

    % code
vel=100;
theta=50;
height=150;
v_vert=vel*sind(theta);  %Y-velocity (m/s)
g=9.81;         %gravity constant (m/s^2)
y_f=-height;
t=0
time=solve('y_f=v_vert*t-g/2*t^2',t)
  end

    % code
  end
and it returns this:
t =

     0

time =

t*v_vert - (g*t^2)/2 %code

Answer 1

[Walter Roberson]

When you pass a quoted string to solve(), existing variables are not used (not unless they were defined within the MuPAD environment, which is not the case for your code).

You should pass in symbolic expressions instead.

syms t
vel=100;
theta=50;
height=150;
v_vert=vel*sind(theta);  %Y-velocity (m/s)
g=9.81;         %gravity constant (m/s^2)
y_f=-height;
time = solve(y_f == v_vert*t-g/2*t^2, t)

Note: if you are using a version of MATLAB that is a couple of years older, it might complain about the == being unable to compare symbolic objects. If that happens, then use the usual trick:

solve( A == B )

is the same as

solve( (A) - (B) )