Question

A block of wood is floating in water at $0^{\circ }C$. Thee temperature of water is slowly raised from $0^{\circ }C$ to ${10}^{\circ }C$. How will the percentage of volume of block above water level change with rise in temperature ?

Answer 1

Water shows anomalous behavior on heating from $0^{0}C$ to $4^{0}C$. Its density unexpectedly increases from $0^{0}C$ to $4^{0}C$ and then decreases. Since for the block, density will decrease on heating, upto $4^{0}C$, fraction of block above water will definitely increase. After that, the decrease in density of water will be more dominant than decrease in density of wood (which is negligible) and hence the portion of block above water will decrease.

Answer is first increases then decreases.