The cube’s mass is x (eg one gram) and its velocity is zero, therefore its momentum (m*v) is zero. Objects in motion tend to stay in motion, while objects at rest (e.g. momentum of zero), tend to stay at rest.
The thing which is moving, is the portal. At best, the event horizon of it reaches the leading-end then the trailing-end of the cube at the speed the portal is moving over the depth of the cube. If the portal moves faster, that distance is covered faster, and the full cube is entirely on the other end of the other portal faster [than a slower moving portal].
Since going through the portal is a frictionless and forceless action, the speed at which the portal fully envelops the cube would neither add nor remove momentum upon it. And if the cube did have its own momentum it would be maintained, but since it does not, the cube would not move until another force, like gravity, acted upon it.
I don’t think this can work. Think through it in several steps rather than just one. Once the cube just started entering the portal, a part of it will already be on the other side, as close to the 2nd portal as possible. When the portal continues moving, more of the cube needs to be on the other side, so it “pushes” the first part of the cube further away. The cube imparts momentum onto itself.
Another way to look at it is using reference frames. It really doesn’t make a difference whether the cube is moving towards the portal or the portal towards the cube. It only matters what the difference of velocity is. The difference of velocity must be maintained on the other side of the portal, and since the 2nd portal is stationary, the cube must move.
PieFed
ThatWeirdGuy1001
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My take:
The cube’s mass is x (eg one gram) and its velocity is zero, therefore its momentum (m*v) is zero. Objects in motion tend to stay in motion, while objects at rest (e.g. momentum of zero), tend to stay at rest.
The thing which is moving, is the portal. At best, the event horizon of it reaches the leading-end then the trailing-end of the cube at the speed the portal is moving over the depth of the cube. If the portal moves faster, that distance is covered faster, and the full cube is entirely on the other end of the other portal faster [than a slower moving portal].
Since going through the portal is a frictionless and forceless action, the speed at which the portal fully envelops the cube would neither add nor remove momentum upon it. And if the cube did have its own momentum it would be maintained, but since it does not, the cube would not move until another force, like gravity, acted upon it.
So, A.
Or, this, but mind blown –> The exit portal would be the thing that moves backwards to maintain the zero momentum of the cube 😅
I don’t think this can work. Think through it in several steps rather than just one. Once the cube just started entering the portal, a part of it will already be on the other side, as close to the 2nd portal as possible. When the portal continues moving, more of the cube needs to be on the other side, so it “pushes” the first part of the cube further away. The cube imparts momentum onto itself.
Another way to look at it is using reference frames. It really doesn’t make a difference whether the cube is moving towards the portal or the portal towards the cube. It only matters what the difference of velocity is. The difference of velocity must be maintained on the other side of the portal, and since the 2nd portal is stationary, the cube must move.