Let m1 be the mass of first block and m2 of second block..
When the system is in equilibrium ..
m2g=kx
2×10=kx
Kx=20
m1g +kx = T
20+20=T
T=40
Now when the string A is cut , we have removed the tension that balances m1g + kx..
This leads to acceleration of the block.
Acceleration= 40/2
=20m/s
Which is the intial acc just after the string is cut.
But when the block comes in contact with m2 and the spring contracts both will fall with the same acc g.
Hope u find it helpful.