when and where the ball will meet the elevator.
Let the ball and the elevator will meet after time t at the level where the ball has an upward displacement x.
For ball : u=18 m/s a=−g=−9.8 m/s2
using S=ut+12at2
∴ x=18t−9.82t2
⟹ x=18t−4.9t2 ..............(1)
For elevator : (7+x)=vt
∴ 7+x=2t
OR 7+18t−4.9t2=2t [using (1)]
OR 4.9t2−16t−7=0
⟹ t=16±√162+4(4.9)(7)2×4.9=3.65 s OR −0.39 s (Not possible)
∴ x=2(3.65)−7=0.3 m
Thus the ball and the elevator will at 12.30 m level after 3.65 s