Question

A ball falls on a wedge the wedge is initially at rest friction is absent every where the collision is elastic

Answer 1

1) Mechanical energy as well as momentum is conserved in all
2) Mechanical energy is conserved but momentum is not conserved in all direction

Answer 2

If the ball falls on the wedge which is initially at rest then the momentum will be conserved only in the horizontal direction.

• When the ball falls on the wedge it is held when there is no pushed outside and has the same and opposite friction, thereby passing the momentum to the ground.
• During the phase, the mechanical energy will also be conserved  but the momentum will not be conserved in all directions and only the horizontal direction.