Answer
$11484375 \ J$
Work Step by Step
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:
$W=\int \rho g A(y) D(y) \ dy\\=\int_0^{2.5} \rho g (2.5-y) (375) \ dy\\=3.125 \times \rho g \times 375\\=11484375 \ J$
