Change floor position in Bounce expression

Darby Edelen and Dan Ebberts helped me cobble this expression together and now I need to modify it in the following way.

I need the ball to bounce ONCE on the floor then I need the floor to fall away. I have tried tying the floor to an expression slider and animating it at the point where I need the change to happen, but this affects the whole animation and just sends the ball hurtling downwards. I just need the floor to act as if it isn't there on the second bounce.

Any help is much appreciated.
With many thanks,
David


Vy0 = 200; //initial y velocity (pixels/second)
seedRandom(index,true);
Vx0 =random(-200,200); // initial x velocity (pixels/second)
g = 2500; // gravity (pixels/second/second)
floor = 1050;
e = .82; //elasticity

b = floor - position[1];
h = b + Vy0*Vy0/(2*g);
T = Vy0/g + Math.sqrt(2*h/g);

if (time < T){
y = Vy0*time - g*time*time/2 + b;
}else{
Vy = -(Vy0 - g*T);
while (true){
Vy *= e;
t = T;
T += 2*Vy/g;
if (time < T){
t = time - t;
y = Vy*t - g*t*t/2;
break;
}else if (T - t < thisComp.frameDuration){
y = 0;
break;
}
}
}
[position[0] + Vx0*time, floor - y]