Let the two masses be m1 and m2, i.e. 2m\;m and k be the spring constant, x be elongation in spring, F be the force experienced by spring and g be acceleration due to gravity. When string 1 is cut, m2 undergoes free fall. ∴ Acceleration of m2 be a2=g and equal force is experienced by m1 ∴mg=2ma1 where, a1 is the acceleration of mass m1, when string is cut ∴‌‌a1=‌