I say its B, because if we jump in a portal we fly out of the other one. Now the difference is here the portal is moving and not the person, but in physics we are only interested in the motion of two bodys relative to each other. If you are standing on the train you would see the portal as stationary and the people coming towards it. Because the object/person enters the portal with speed it also comes out with the same speed.

[–] blurr11@programming.dev 1 points 1 year ago

But the object doesn't enter at speed here it's stationary. If a hoop is thrown at an object and passes around the object the object is still stationary. The speed of the portal relative to the object does not impart movement on the object.

The quicker the portal moves the quicker the object appears on the other side but for the object to shoot out it means energy is being transfered from the car to the object.

If you're right then what happens If the two portals are moving at equal and opposite speeds?