A bullet of mass 0.2 kg is fired into a fixed vertical barrier. It enters the barrier horizontally with speed \(250 \mathrm{~m} \mathrm{~s}^{-1}\) and emerges horizontally after a time \(T\) seconds with speed \(40 \mathrm{~m} \mathrm{~s}^{-1}\). There is a constant horizontal resisting force of magnitude 1200 N . Find \(T\).