Two blocks A and B of same mass m attached with a light spring are suspended by a string as shown in fig. Find the acceleration of block A and B just after the string is cut.

Explanation

When block A and B are in equilibrium position

when string is cut, tension T becomes zero.But spring does not change its shape just after cutting. So spring force acts on mass B, again draw F.B.D. of block A and B as shown in figur.e
F.B.D. of 'B'

F.B.D. of 'A'
`mg + T_(0)= m.a_(A)`
`2mg =m.a_(A0`
`a_(A) = 2g ` ( downwards )