When the left rope is vertical, the tension between the ball on the rope and the slider is mg, which is equal and the system is balanced.

According to geometric knowledge, the distance from C to C is 2L;

When the sliding distance of the slider is l, let its speed be vA,

At this time, the speed of ball B is vB, so: vB=vAcosθ.

The conservation of mechanical energy of the system during the falling of the small piece A is obtained by the law of conservation of mechanical energy:

mglsinθ= 12 MVB 2+ 12 MVA 2

Solution: v = 43gl5

So the answer is: 2L, 43gL5. ..