block in elevator

Idea is that acceleration of the lift is 12m/s² which is greater

than acceleration due to gravity. Hence, when lift starts descending

with this acceleration, block loses contact with the floor and starts

falling under the action of gravity.

Thus, acceleration of the block = acceleration due to gravity = 10 m/s² (downward)

Hence using s = ut + ½ at² along downward direction, we
have s = 0 x 0.2 + ½ x 10 x 0.2²

i.e. s = 0.2 m = 20 cm.

thanx