Determine:

1) The horizontal acceleration of the wedge

2) The horizontal acceleration of the block

3) The vertical acceleration of the block

I don't know how to solve any of these.. I've applied Newton's laws, but I get only 3 equations. I'm guessing there's some additional constraint which gives me the fourth one, but I haven't been able to find it. Should I try Newton's laws in laboratory coordinates?

This is what I know so far :

1) The wedge accelerates horizontally to the left ( by the normal b/w wedge,block)

2) The block accelerates horizontally to the right ( by the normal b/w wedge,block)

3) The block accelerates downwards vertically ( I don't know how to reason this one.. perhaps because if it didn't accelerate downward vertically, then it would lose contact with the wedge, but I'm not sure)

4) The centre of mass of the system remains stationary horizontally as all the horizontal forces are internal, so they're cancelled out by Newton's 3rd law.

5) If the block accelerates vertically, and the wedge stays on the same vertical level, then the centre of mass of the system accelerates vertically.

Please help.