2. (15 points) A wooden cube with edge $\ell=30$ cm floats in a lake. The density of wood $\quad \rho=750 \mathrm{kg} / \mathrm{m}^{3}, \quad$ the density of water $\rho_{0}=1000 \mathrm{kg} / \mathrm{m}^{3}$. What is the minimum work required to completely pull the cube out of the water?
2. In equilibrium $m g=\rho_{0} g \frac{3}{4} \ell^{3}$

External minimal force at each moment in time

$$
F=m g-F_{\mathrm{Apx}}=\rho_{0} g \frac{3}{4} \ell^{3}-\rho_{0} g \ell^{2}\left(\frac{3}{4} \ell-x\right)=\rho_{0} g \ell^{2} x,
$$

where $x$ is the height of the lift at that moment. The external force depends linearly on the height of the lift, so the work done by this force is equal to the area of the figure (triangle) on the $F(x)$ diagram

$A_{\text {min }}=\frac{1}{2} \frac{3}{4} \rho_{0} g \ell^{3} \frac{3}{4} \ell=\frac{9}{32} \rho_{0} g \ell^{4}=22.8$ J.

(15 points)