Question

A block of wood is floating on water at $O^0$C, with a certain volume V above water level. The temperature of water is slowly raised from $O^0$ C. How will the volume V change with the rise of temperature?

• A. V will be unchanged
• B. V will decrease from $O^0$ C
• C. V will decrease till $4^0$ C and then increase
• D. V will increase till $4^0$ C and then decrease

Answer 1

The correct option is D V will increase till $4^0$ C and then decrease

Volume above water level

Let $x$ be the volume immersed in the water

Buoyant force $=x\times {\rho }_{water}\times g$

Now, till $4^{o}C$; ${\rho }_{water}$ increases, so $x$ decreases

$\Rightarrow$ as $x$ decreases, $V$ increases

After $4^{o}C$; ${\rho }_{water}$ decreases, so $x$ increases

$\Rightarrow$ as $x$ increases, $V$ decreases