i believe the answer is A and there is no energy being transferred from the piston to the box. all the energy it transferred to the platform below as the piston crashes on the platform.
I wasn't exactly sure where to post this. 'Puzzles' seems like the best place.
First take a look at the picture. A moving platform with a portal is speeding downwards towards a stationary platform on which a cube is placed.
The exit portal is placed on a slope nearby.
What will happen when the moving portal (on platform) consumes the cube?
A - the cube will slide down the slope at the exit portal
B - the cube will be launched out of the exit portal at great speed
I believe both outcomes are possible, depending on the speed of the platform.
Since we're thinking with portals, we can assume the conservation of momentum (if you trust a crazy computer-robot-thing). All you have to do is to switch reference frames, for easier visualisation. Think of the platform with the portal as stationary and the platform with the cube moving upwards.
The cube's initial speed as it exits the blue portal will be the same as its speed entering the yellow portal. Whether it plops out as in A or flies out as in B depends solely on the speed of the moving platform.
If the platform speed is low, the cube plops out as in A, as gravitational force pulls it down quickly. If the platform speed is high, it will fly out further until gravity takes over. The reasoning in this little paragraph is based on basic projectile motion, or if you wish, conservation of energy (ignoring the fact that there are portals...).