You missed an important part of the question bro. You forgot to include the angle of the wedge which have to be 45 degree to get your answer.
Initial energy is mgH
Final Kinetic energy at an intermediate height h is : 1/2Mv2 + 1/2Mv2 + mgh + 1/2m(v1)2
The velocity of two wedges are same by symmetry and i considered it to be v.
The velocity of the rod (v1) have to be found by geometry. As the angle of the wedge is 45 degree, v1 will also be v. As the angle of the wedge is 45, the velocity of the rod is also v by common sense. But if the angle is not 45 , eg 30 i am not able to find the velocity of the rod by geometry. Please tell me how to do it.
Therefore as v1 = v .
1/2Mv2 + 1/2Mv2 + mgh + 1/2m(v)2 = Mv2 + mgh + 1/2mv2 = Final energy
By energy conservation (initial energy = final energy )
mgH = Mv2 + mgh + 1/2mv2
mg(H-h) = v2 (2M + m)/2
v = ( 2mg(H-h) / (2M + m) )1/2
Velocity of recede of the two wedges is 2v as both are going in opposite direction.
Therefore, answer = 2v = ( 8mg(H-h) / (2M + m) )1/2
Hence the answer is proved. Wheres my rate bro ?