A cork is submerged in water by a spring attached to the bottom of a pail. When the pail is kept in a elevator moving with an acceleration downwards, the spring length

Density of cork = d, Density of water = ρResultant upward force on cork =V(ρ−d)gThis causes elongation in the spring. When the lift moves down with acceleration a, the resultant upward force on cork =V(ρ−d)(g−a)which is less than the previous value. So the elongation decreases.