A uniform rod `OB` of length `1m`, cross-sectional areal `0.012 m^(2)` and relative density `2.0` is free to rotate about smooth hinge `O` in vertical plane. The rod is held with a horizontal string `AB` which can withstand a maximum tension of `45N`. The rod and string system is kept in water as shown in figure. The maximum value of angle `alpha` which the rod can make with vertical without breaking the string is