Correct Answer - 2
Consider motion of two balls with respect to rocket.
Maximum distance of ball A from left wall
`(u^(2))/(2a)=(0.3xx0.3)/(2xx2)=(0.09)/(4)=0.02m`
So, collision of two bals will take place very near to left wall.
For `BS=ut+(1)/(2)at^(2)`
`-4=-0.2t((1)/(2))2t^(2) rArr t^(2)+0.2t-4=0`
`rArrf t=(-0.2+-sqrt(0.04+16))/(2)=1.9`
nearest integer=2s.