Let us make a few assumptions before solving the problem as stated below:

1. After collision the block moves along the surface of wedge with respect to it.

2. The wedge moves in horizontal direction.

Let us assume x-aixis along the surface of wedge and y-axis along normal to the surface of wedge.

From FBD of block:

Applying conservation of momentum along x-axis:

....................................(1)

Along y-axis:

....................................(2)

From FBD of wedge:

.........................................................................(3)

Solving above equations for V12 we get

:

Once relative velocity of block with respect to wedge is found at t=0, now we will try to find Relative acceleration of block wrt wedge.

See next part of solution.