The block of mass $m$ slides on a wedge of mass $m$ which is free to move on the horizontal ground. Find the acceleration of wedge and block.
Let $a$ acc. of wedge and $b$ acc. of block w.r.t. wedge. Applying Newton Laws of motion in $x$ direction,
But why $F_x=0$, if it is then how can a system can have acceleration in $x$ direction, they not massless too?