Question

Which has a greater buoyant force on it, a 25.0 cm3 piece of wood floating with part of its volume above water or a 25.0 cm3 piece of submerged iron?

Answer 1

Answer:

piece of submerged iron

Explanation:

The buoyant force is given by:

$B=\rho_L V_{sub} g$

where

$\rho_L$ is the density of the liquid (in this case, water)

$V_{sub}$ is the submerged part of the object

g is the acceleration due to gravity

In this problem, the liquid used in the two examples is the same, water, so $\rho_L$ is the same; and g is the same as well. Therefore, the only difference between the two examples is $V_{sub}$.

For the piece of wood, we are told that the object is floating, so only a fraction of its total volume of 25.0 cm3 will be submerged: therefore the submerged volume will be less than 25.0 cm3. On the contrary, the problem tells us that the piece of iron is submerged, so the submerged volume in this case is 25.0 cm3. Therefore, the submerged volume for the iron is greater than for the piece of wood, so the buoyant force of the piece of iron is greater.