# A tank with vertical sides is square in plane with 3m long sides.The tank contains oil of relative density 0.9 to a depth of 2.0m which is floating on water a depth of 1.5m.Calculate the force on the walls.(Consider one wall of the tank).

$\begin{array}{1 1}(A)\;791461N\\(B)\;153.4N\\(C)\;141N\\(D)\;165544N\end{array}$

Density of oil $\rho_{oil}=0.9$
$\rho_{water}=900Kg/m^3$
Force/length,F=Force under graph
$\Rightarrow$ Sum of the areas
$\Rightarrow f_1+f_2+f_3$
$f_1=\large\frac{(900\times 9.81\times 2)\times 2}{2}$$\times 3=52974N f_2=(900\times 9.81\times 2)\times 1.5\times 3=79461N f_3=\large\frac{(1000\times 9.81\times 1.5)\times 1.5}{2}$$\times 3=33109N$
$F=f_1+f_2+f_3$
$F=(52974+79461+33109)N$
$F=165544N$
Hence (D) is the correct answer.