
Originally Posted by
Sylvrdragon
Portal puzzle: B.
The cube will exit the stationary blue portal at the speed of the piston. As far as the blue portal is concerned, the block didn't exist before it exited, hence, its previous state doesn't matter. Besides, momentum and velocity is relative.
Imagine that you're only watching the blue portal. Suddenly, the cube would emerge from it at the speed of the piston. Why would it stop moving? The state it was in on the other side of the portal doesn't matter.
A portal is merely a hole that connects different points of space, not an object capable of generating force. It has no mass and no volume. It doesn't destroy the object going in and re-create it going out. It simply connects previously un-connected points. It only conserves momentum the same way a door conserves momentum when you walk through it. In your scenario, you could slap a portal on a 1kg piece of drywall, drop it on a 100kg steel ball, and essentially generate infinite free energy, which assrapes physics even worse than portals already do. If someone drops a hula-hoop off a building onto you, you don't fly to the top of the building when it lands. Also, the plane takes off, but only if its bearings are made of unobtainium.