Two blocks, of masses 2m and 3m, are connected by a light string of length 2L. Both blocks can slide freely along a horizontal bar. A block of mass m is attached to the midpoint of the string.

Initially, the string is straight, and all three blocks are held at rest, as shown. Then the blocks are released simultaneously. Find the speeds of blocks 2m and 3m immediately before they collide. The acceleration due to gravity is g.

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