Two crates $A$ and $B$, of mass 5 kg and 4 kg respectively, are connected by a light inextensible rope that passes over a smooth pulley at the top of a symmetrical wedge. The wedge is fixed to the floor, with both faces inclined at an angle of $45^{\circ }$ to the horizontal. Crate $A$ is on a smooth face, while crate $B$ is on a rough face where the coefficient of friction is 0.2. The rope remains taut throughout the motion.