## Calculus (3rd Edition)

$$105840 \mathrm{J}$$
The volume of one layer is 4 $\Delta y \mathrm{m}^{3}$ and so the weight of one layer is $23520 \Delta y$ N. Thus, the work done against gravity to build the tower is \begin{align*} W&=\int_{0}^{3} 23520 y d y\\ &=\left.11760 y^{2}\right|_{0} ^{3}\\ &=105840 \mathrm{J} \end{align*}