Water flows through a vertical tube of variable cross section. The area of cross - section at A and B are 6 mm2 and 3 mm2 respectively. If 12 cm3 of water enters per second through A, find the pressure difference |PA−PB|. The separation between the cross-section at A and B is 100 cm. (Take density of water as 1000 kg/m3 and g=10 m/s2)