Two identical blocks, each having mass M, are placed as shown in figure. These two blocks A and B are smoothly conjugated, so that when another block C of mass m passes from A to B there is no jerk. All the surfaces are frictionless, and all three blocks are free to move. Block C is released from rest, then

When block C is released from rest, it slides down on A, pushing it against the wall (because of a component of normal force between A and C), as on left of A a wall is there, it does not move. The kinetic energy of block C increases and it becomes mgh when it is just going to pass on B.When block C comes in contact with B, due to horizontal component of normal force between C and B, B starts moving towards right and kinetic energy of C gets converted into kinetic energy of B and potential energy of C, so block C is not able to reach the topmost point of B. Then block C starts sliding down B, but velocity of B will still be increasing and becomes maximum when C reaches its bottom-most point and is moving left.