My Fish Food Won't Fall

Ok I admit it, I'm a noob and a spaz and all those fun things. This is my first programming assignment and not a single part of it has worked well for me. I've finally made it to the food falling bit and it won't do it. My teacher even gave me better code and it still won't fall. I have my dynamic fields, I've set the world limits. I've named my class and it still won't fall. The project is due this Sunday and I've been trying to get it to fall since last Sunday. What am I doing wrong?

function FishFood::onLevelLoaded(%this, %scenegraph)
{
%this.startPosition = %this.getPositionY();
%this.setLinearVelocityY(getRandom(%this.minSpeed, %this.maxSpeed));
}

function FishFood::onWorldLimit(%this, %mode, %limit)
{
if(%limit $="bottom")
{
%this.spawn();
}
}

function FishFood::spawn(%this)
{
%this.setPosition(getRandom(-50,50), %this.startPositionY);
%this.setLinearVelocityY(getRandom(%this.minSpeed, %this.maxSpeed));
}