Trying to plot a D2z function

I am trying to plot the funtion produced by the Dsolve function but it comes up with Not enough input arguments, can I please get any help, Start it Cycloid(3,3,10)

function Cycloid(h,Q,tf)

g=9.81;

% Making the Brachistochrome Equation in MatLab

r=@(z)((3.14.*Q)-(Q).*(acos((z./Q)-1))+sqrt(z.*(2.*Q-z)));

% This is now inputting the second derivitive of z and the first derivitive

% of r

f=@(t,z)[z(2);(-g/Q)*(z(1)-(h./2)) ; sign(z(2)).*(sqrt((g./Q).*(h-z(1)).*(2.*Q-z(1))))];

ode23(f,[0 tf],[h;0;r(h)])

syms t;

j=dsolve('D2z=-(g/Q)*(z(1)-(h/2))','z(0)=h',t)