Right answer is (a) 2943kN
Explanation: Given,
Discharge q=0.04 m^3/s
z=12m
Area A=50 m^2
coefficient of permeability k=1.6*10^-3m/s
the hydraulic gradient i is given by,
i=q/(kA)
i=0.04/(50*1.6*10^-3)
i=0.5
The seepage force J is given by,
J= iγwzA
J=0.5*12*9.81*50
∴ J=2943kN.