A rocket is moving in a gravity free space with a constant acceleration of $2 \mathrm{~ms}^{-2}$ along $+x$ direction (see figure). The length of a chamber inside the rocket is 4 m . A ball is thrown from the left end of the chamber in $+x$ direction with a speed of $0.3 \mathrm{~ms}^{-1}$ relative to the rocket. At the same time, another ball is thrown in-x direction with a speed of $0.2 \mathrm{~ms}^{-1}$ from its right end relative to the rocket. The time in seconds when the two balls hit each other is: