How to remove a movieclip once its done playing

programming flash
1

I need to know how to removed a movieclip when its done playing, I attancht it like this, to play, but it just keeps playing, here is the code con the main timeline:

if( mob.hitTestPoint(hero.x,hero.y,true)){
		var boom:MovieClip = new explosion();
     boom.x=mob.x;
     boom.y=mob.y;
     stage.addChild(boom);
     if(this.contains(mob)){
     removeChild(mob);
							 }
		}

And the other thing is I need my hero to go to the next frame (a new level) when it hits another thing… (All of this in Actionscript 3.0)
Please help me!!