Science: Fluid Mechanics: Pressure and Buoyancy Worksheet

Question 1

A force of 240 N is applied evenly over an area of 0.80 m^2. What pressure is produced?

Accepted Answer

The pressure is 300 Pa because pressure equals force divided by area, so 240 N divided by 0.80 m^2 equals 300 N/m^2, which is 300 Pa.

Question 2

A diver is 15 m below the surface of fresh water. If the density of water is 1000 kg/m^3 and g = 9.8 m/s^2, what fluid pressure is due to the water alone at that depth?

Accepted Answer

The fluid pressure due to the water is 147,000 Pa because pressure in a fluid is rhogh, so 1000 x 9.8 x 15 = 147,000 Pa.

Question 3

Explain why the pressure in a fluid increases with depth.

Accepted Answer

Pressure increases with depth because deeper layers of fluid must support the weight of more fluid above them. As a result, the force on a given area becomes greater lower in the fluid.

Question 4

A hydraulic lift has a small piston with an area of 0.020 m^2 and a large piston with an area of 0.40 m^2. If a force of 150 N is applied to the small piston, what force is produced on the large piston?

Accepted Answer

The force on the large piston is 3000 N. By Pascal's principle, the pressure is the same in both pistons, so F2 = F1 x A2/A1 = 150 x 0.40/0.020 = 3000 N.

Question 5

State Archimedes' principle in your own words.

Accepted Answer

Archimedes' principle states that an object in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

Question 6

A block is fully submerged in water and displaces 0.025 m^3 of water. What buoyant force acts on the block? Use a water density of 1000 kg/m^3 and g = 9.8 m/s^2.

Accepted Answer

The buoyant force is 245 N because the buoyant force equals the weight of the displaced water: F_b = rhoVg = 1000 x 0.025 x 9.8 = 245 N.

Question 7

An object weighs 60 N in air and has an apparent weight of 45 N when submerged in water. What is the buoyant force on the object?

Accepted Answer

The buoyant force is 15 N because buoyant force equals the loss of weight in the fluid, and 60 N minus 45 N equals 15 N.

Question 8

A metal cube has a density of 7800 kg/m^3. Will it float or sink in water? Explain your answer.

Accepted Answer

The cube will sink in water because its density is much greater than the density of water, which is about 1000 kg/m^3. Objects denser than the fluid sink if no other support force acts on them.

Question 9

A piece of wood has a density of 600 kg/m^3 and is placed in water. What fraction of its volume will be submerged when it floats?

Accepted Answer

The wood will have 0.60, or 60 percent, of its volume submerged. For a floating object, the fraction submerged equals the object's density divided by the fluid density, so 600/1000 = 0.60.

Question 10

Why does a steel ship float even though steel is denser than water?

Accepted Answer

A steel ship floats because its overall average density, including the air-filled interior, can be less than the density of water. The ship displaces enough water for the buoyant force to balance its weight.

Question 11

A balloon contains helium, which is less dense than air. Explain why the balloon rises.

Accepted Answer

The balloon rises because the air around it exerts a buoyant force equal to the weight of the displaced air. If that buoyant force is greater than the total weight of the helium and the balloon material, the balloon accelerates upward.

Question 12

A submarine takes in water into its ballast tanks before diving. Explain how this changes its buoyancy.

Accepted Answer

Taking in water increases the submarine's mass and average density. This reduces its net buoyancy, and if its weight becomes greater than the buoyant force, the submarine sinks. Releasing water and replacing it with air lowers its average density and increases buoyancy.

Science: Fluid Mechanics: Pressure and Buoyancy

Science: Fluid Mechanics: Pressure and Buoyancy

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