Review on Fluids - AP Physics 1

An object is fully submerged in water and experiences a buoyant force equal to:

• A. Its own weight

• B. The weight of the displaced water

• C. Its volume multiplied by its density

• D. The atmospheric pressure

Answer explanation

The buoyant force on a fully submerged object equals the weight of the water it displaces, according to Archimedes' principle. Therefore, the correct answer is B, the weight of the displaced water.

If an object floats in a fluid, the buoyant force equals:

• A. Zero

• B. The volume of fluid displaced

• C. The weight of the object

• D. The density of the fluid

Answer explanation

The buoyant force on a floating object equals the weight of the object. This is due to Archimedes' principle, which states that the upward buoyant force is equal to the weight of the fluid displaced by the object.

Archimedes’ Principle states that:

• A. Fluid pressure is the same at all depths

• B. The buoyant force equals the object’s weight

• C. The buoyant force equals the weight of displaced fluid

• D. Objects sink if they’re denser than water

Answer explanation

Archimedes' Principle states that the buoyant force on an object submerged in a fluid is equal to the weight of the fluid it displaces. Therefore, the correct answer is C, as it directly describes this relationship.

What happens when something is less dense than water?

• A. It floats

• B. It sinks

• C. Nothing

Answer explanation

When an object is less dense than water, it displaces a volume of water equal to its weight, causing it to float. Therefore, the correct answer is A. It floats.

The SI unit of density is:

• A. kg

• B. m³

• C. kg/m³

• D. N/m²

Answer explanation

The SI unit of density is defined as mass per unit volume. Therefore, it is expressed as kilograms per cubic meter, which is kg/m³. This makes option C the correct answer.

A 2 m³ block has a mass of 1000 kg. Its density is:

• A. 5000 kg/m³

• B. 2000 kg/m³

• C. 500 kg/m³

• D. 2 kg/m³

Answer explanation

Density is calculated as mass divided by volume. Here, density = 1000 kg / 2 m³ = 500 kg/m³.

Pressure in a fluid increases with:

• A. Surface area

• B. Depth

• C. Temperature

• D. Height above the surface

Answer explanation

Pressure in a fluid increases with depth due to the weight of the fluid above. As you go deeper, there is more fluid pressing down, resulting in higher pressure. Therefore, the correct answer is B. Depth.

The SI unit of pressure is:

• A. Newton

• B. Pascal

• C. Joule

• D. Bar

Answer explanation

The SI unit of pressure is the Pascal (Pa), which is defined as one newton per square meter. It measures force applied over an area, making option B the correct choice.

A submarine sinks when:

• A. Its density decreases

• B. Buoyant force increases

• C. Weight exceeds buoyant force

• D. Displacement increases

Answer explanation

A submarine sinks when its weight exceeds the buoyant force acting on it. This means that the force pushing it up is not enough to counteract its weight, leading to sinking.

Bernoulli’s principle explains that as fluid speed increases, pressure:

• A. Increases

• B. Decreases

• C. Remains constant

• D. Is zero

Answer explanation

According to Bernoulli’s principle, as the speed of a fluid increases, the pressure within the fluid decreases. Therefore, the correct answer is B. Decreases.