Answer
$1.4 \times 10^7 \ J$
Work Step by Step
The area of a slice is equal to $A(y)=(25)(15)=375$
We need to use the formula such as: $W=\int_a^b \rho g A(y) D(y) \ dy$.
Plug in the above formula the given values to obtain:
$W=\int_a^b \rho g A(y) D(y) \ dy\\=375 \int_0^{2} \rho g (3-y) \ dy\\=375 \times \rho g \times [3y-\dfrac{y^2}{2}]_0^2 \\=(375)(4) \rho g\\=(375) (1000) (9.81) (4)\\=1.4 \times 10^7 \ J$
