I know a car's starting speed and deceleration rate. How can I calculate the stopping time in the code?

So I plotted a car's forward speed by time plot and I calculated it's deceleration rate by the plot. I know it stops at 74.967 seconds but I don't know how to implement and show it in this code. What should I add? Deceleration rate is 0.4 m/s^2. Should I write another code with these values or can I add it directly to this and if so how?

ti=0.0; tf=15.0; ui=30.0;

m=2585; g=10; W=m*g; Theta=0.0; Fx=0;

f=0.03; rho=1.225; Cd=0.2; A=2.9; uw=0.0;

tol=1.0E-4; trace=1;

options = odeset('RelTol',tol,'AbsTol',tol);

[t,u]= ode23(@(t,u)asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw),[ti,tf],ui,options);

plot(t,u,"r")

title("Vehicle Forward Speed");

xlabel("Time(sec)")

ylabel("u(m/sec)"); grid;

function udot = asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw)

if u>0

udot=(1/m)*(Fx-W*sin(Theta)-f*W*cos(Theta)-0.5*rho*Cd*A*(u+uw)^2);

else

udot=0;

end

end

Answer 1

[Askic V]

Well, your deceleration rate is not constant and what I see from the code it starts with -0.4237 m/s^2 and ends with -0.3 m/s^2, your vehicle will not stop at 75 sec. It would have if deceleration rate had been constant.

If you put tf to be 100 sec, you can see that it will stop around 89 sec

ti=0.0; tf=100.0; ui=30.0;
m=2585; g=10; W=m*g; Theta=0.0; Fx=0;
f=0.03; rho=1.225; Cd=0.2; A=2.9; uw=0.0;
tol=1.0E-4; trace=1;
options = odeset('RelTol',tol,'AbsTol',tol);
[t,u]= ode23(@(t,u)asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw),[ti,tf],ui,options);
plot(t,u,"r")
title("Vehicle Forward Speed");
xlabel("Time(sec)")
ylabel("u(m/sec)"); grid;

tstop =t(find(u<=0, 1,'first'))

tstop = 88.9015

function udot = asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw)
    if u>0
        udot=(1/m)*(Fx-W*sin(Theta)-f*W*cos(Theta)-0.5*rho*Cd*A*(u+uw)^2);
    else
        udot=0;
    end
end