There's a block slides downward along a frictionless wedge which sits on a frictionless horizontal surface, when the block leaves the wedge, both of the wedge and the block have a horizontal velocity in opposite direction.
In this situation,can we say the momentum of the system is conserved? How to deal with the vertical motion of the block? If I say the system is conserved, should the system include earth? Since the force of gravity of the block as an external force of the block-wedge system has done work during the motion.
Any idea or hint is appreciated!