move A-->B ...What about entropy change?

Hi,
I have a physical question regarding entropy, temperature, internal energy and mechanical energy.
The situation is following: Two objects are located inside a one dimensional frictionless and adiabatic space where object “a” is an observer that makes object “b” to move an increment into one direction via a force. (Obviously observer “a” has to move the same increment into the opposite direction). After that process both objects shall stay at fixed places for ever.

If we calculate the change of mechanical energy that the observes has to invest to make object “b” to move an increment then the energy change is zero because the force that the observer has build up against “b” to accelerate it into one direction is completely recycled because of deceleration at the end of the increment.

However this is also the point were I am unsure because I am not able to answer whether entropy and energy do change during that process or not. I would say no because internal energy has to stay constant but I hope that someone else here could give a better explanation or a hint.

A similar question regarding this is: Did the observer requires energy to make the process working ?

Best Regards,
bolly