1. The buoyant force acts on the body immersed in liquids and gases.
2. The buoyant force depends on the densitydensitydensity of the liquid and the volumevolumevolume of the immersed part of the body. This force does not depend on the shape of the body, its mass, liquid volume.
3. For each body immersed in a liquid (or gas), there is a buoyant force that is directed upwards and equal in magnitude to the weight of the displaced liquiddisplaced liquiddisplaced liquid (or displaced gas).
4. The buoyant force has a vertical upward direction.

1. The gravitational force ($\overrightarrow{Q}$) and the buoyant force ($\overrightarrow{F_B}$) act on the emerging block.
2. There are various relationships between the buoyant force and the gravitational force:
a) when the block emerges, the magnitude of the buoyant force is greater than the magnitude of the gravitational force,
b) when the block is emerging (floats partially immersed), the gravitational force is balanced by the buoyant force - the magnitudes of these forces are equal.
3. The weight of the liquid displaced by the body ($\overrightarrow{F_B}$) is larger than the weight of the immersed body ($\overrightarrow{Q}$). Since the volume of the displaced liquiddisplaced liquiddisplaced liquid and the volumevolumevolume of the immersed body are the same, it can be concluded that the density of the liquid is larger than the density of the body.

1. The gravitational force ($\overrightarrow{Q}$) and buoyant forcebuoyant forcebuoyant force ($\overrightarrow{F_B}$) act on the floating block completely immersed in the liquid.
2. The magnitudes of the gravitational force ($\overrightarrow{Q}$) and buoyant force ($\overrightarrow{F_B}$) are equal.
3. The weightweightweight of the liquid displaced by the body ($\overrightarrow{F_B}$) is equal to the weight of the immersed body ($\overrightarrow{Q}$). Since the volume of displaced liquid and the volume of the immersed body are the same, it can be concluded that the density of the liquid is equal to the density of the body.

1. The gravitational force ($\overrightarrow{Q}$) and buoyant force ($\overrightarrow{F_B}$) act on the block sinkingsinkingsinking in the liquid.
2. The magnitude of the gravitational force ($\overrightarrow{Q}$) is greater than the magnitude of the buoyant force ($\overrightarrow{F_B}$).
3. The weight of the liquid displaced by the body ($\overrightarrow{F_B}$) is smaller than the weight of the immersed body ($\overrightarrow{Q}$). Since the volume of the displaced liquiddisplaced liquiddisplaced liquid and the volumevolumevolume of the immersed body are the same, it can be concluded that the densitydensitydensity of the liquid is smaller than the density of the body.

1. Yes. There is a buoyant force acting on each of the bodies depicted in the photos.
2. Smaller buoyant force acts on the submarine (Photo 2).
3. In Photos 3 and 5 the buoyant force is larger than the gravitational force.
4. The buoyant force may be equal to the gravitational force in Photos 1 and 4.
5. In order for the submarine to emerge, it would be necessary to empty the ballast tanks, i.e. pump out the water from these tanks replacing it with gas.

a) True.
b) False.
c) True.

Since the balloon floats freely in the air, the buoyant force in the air is equal to the weight of the balloon. Since the weight of the air displaced by the balloon is equal to the weight of this balloon, its density $d_B$ must be equal to the density of air $d_A$.

$Q=m_B\cdot g=d_B\cdot V_B\cdot g=1,29\frac{kg}{m^3}\cdot 250m^3\cdot 10\frac{m}{s^2}=3225N$

The iron block sinks in water because water density ($d_w=1\frac{g}{c{m}^3}$) is almost eight times smaller than the iron density ($d_i=7,8\frac{g}{c{m}^3}$). The buoyant force equal to the weight of the displaced water is therefore smaller than the weight of the iron block. The iron block floats in mercury because the mercury density ($d_M=13,6\frac{g}{c{m}^3}$) is almost twice as high as the iron density ($d_i=7,8\frac{g}{c{m}^3}$). The buoyant force equal to the weight of the displaced mercury, when the iron block is completely immersed in mercury, is therefore larger than the weight of the iron block. Thus, a block made of iron must come up  to the surface of mercury.