A tank is filled with water of density 1 g per cm3  and oil of density0.9 g per cm3 . The height of water layer is 100 cm  and of the oil layer is400 cm . If g=980 cm/sec2 , then the velocity of efflux from an opening in the bottom of the tank is:

Let dw  and d0  be the densities of water and oil, then the pressure at the bottom of the tank =hwdwg+h0d0g Let this pressure be equivalent to pressure to water of heighth . Then,hdwg=hwdwg+h0d0g ∴  h=hw+h0d0dw=100+400×0.91 =100+360=460 According to Torricelli’s theorem,v=2gh=2×980×460cc/sec =920×980 cc/sec