A bullet of mass $200 \mathrm{~g}$ having initial kinetic energy $90 \mathrm{~J}$ is shot inside a long swimming pool as shown in the figure. If it's kinetic energy reduces to $40 \mathrm{~J}$ within $1 \mathrm{~s}$, the minimum length of the pool, the bullet has to travel so that it completely comes to rest is