2. Gavriil and Glafira took a glass filled to the brim with water and poured a little water into three ice cube trays, then placed them in the freezer. When the ice froze, the three resulting ice cubes were put back into the glass. Gavriil predicted that some water would spill out of the glass because ice expands in volume when it freezes. Glafira, however, claimed that the water level would be below the rim of the glass because part of the floating ice would protrude above the water surface. Who is right and why?
Answer: No one is right. The water will fill the glass exactly to its edges.

Instructions. Let $V$ be the volume of water in the molds. Then the volume $W$ of ice in the molds can be determined from the law of conservation of mass $V \cdot \rho_{\text {water }}=W \cdot \rho_{\text {ice }}$. When the ice of volume $W$ is floating, the submerged part of this volume $U$ can be determined from the condition of floating bodies $U \cdot \rho_{\text {water }}=W \cdot \rho_{\text {ice }}$. It is therefore clear that $V=U$.