as the area of cross section of the tank is large compared to that of the opening, the speed of water in the tank will be very smal as compared to the speed at the opening. The pressure at the surface of water in the tank is that due to the atmosphere plus due to the load.
`P_A=P_0+((20kg)(10ms^-2))/(0.5m^2)=P_0+400Nm^-2`
At the opening the pressure is that due to the atmosphere,.
Using Bernoulli equation
`P_A+rhogh+1/2rhov_A^2=P_B+1/2rhov_B^2`
`or, P_0+400Nm^-2+(1000kgm^-3)(10ms^-2)(0.5m)+0`
`=P_0+/2(1000kgm^-3)v_B^2`
`5400Nm^-2=(500kgm^-1)v_B^2`
`or `v_B=3.3ms^-1`