It’s not impossible because portals can’t exist, that’s a strawman I compared it to a hula hoop and informed u that the bottom half of a hula hoop can’t fall while the top half stays still, learn it it’s simple.

Next, the block factually has no momentum, lots of things r relative and can seem different than they r. The box is still, has no momentum. I’m informing u of that it’s a fact. A portal moves over the block, and now causing the block to move while it continues moving does not follow the conservation of energy, you are creating energy. Box not moving, now it is, simple as that. Factually A supports the conservation of energy, u can say it’s the opposite but idk how that works when ur solution creates energy