Deck 11: Static Fluids

Question 1

A wooden log floats in a river (density 1000 kg/m³), with one-quarter above the water, carried toward the sea (density 1025 kg/m³) by the river current. What will be the change in the percentage of the volume of log above water when it comes to the sea?

A)The log will go up 2%.
B)The log will go down 2%.
C)The log will go up 27%.
D)The log will go down 27%.

Answer 1

The log will go up 2%.

Question 2

What is the transmural ratio between a soap bubble of diameter D and another one with double the diameter, 2D?

A)The pressure in a bubble with diameter D is 2 times larger than in the 2D bubble.
B)The pressure in a bubble with diameter D is 2 times smaller than in the 2D bubble.
C)The pressure in a bubble with diameter D is 2ð times larger than in the 2D bubble.
D)The pressure in a bubble with diameter D is 2ð times smaller than in the 2D bubble.

Answer 2

The pressure in a bubble with diameter D is 2 times larger than in the 2D bubble.

Question 3

If, in an unknown liquid, we measure pressure of 1.2 atm at 0.15 m depth, at what depth will the pressure measure 2.4 atm?

A)0.08 m
B)0.30 m
C)1.05 m
D)2.10 m

Answer 3

1.05 m

Question 4

A rock is sinking in the water. Which one of these statements correctly describes the buoyant force?

A)It is zero.
B)It is equal to the weight of the wood.
C)It is equal to all the other forces acting on the wood, but opposite in direction.
D)It is equal in magnitude but opposite in direction of the weight of the wood.

Question 5

If P is a pressure, ñ density, g gravitational acceleration, and h height (or depth) of a fluid, where is the relationship P = ñgh applicable?

A)only in liquids
B)only in gases
C)only in gases of uniform density (ideal gases)
D)in any type of fluid with uniform density (ideal fluid)

Question 6

An iceberg has a density 917 kg/m³, and seawater has a density 1025 kg/m³. What fraction of the iceberg is under the surface of the water?

A)9.3%
B)10.5%
C)89.5%
D)90.7%

Question 7

An air bubble is 50 cm below the surface of a lake. In that case, we assume that the bubble has only one surface to generate surface tension. The gauge pressure inside the bubble is 6.0 × 10³ Pa. What is radius of the bubble? (The density of the water is ñ_H2O = 1000 kg/m³, and the surface tension is ó = 0.073 N/m.)

A)2.6 × 10^-4 m
B)1.3 × 10^-4 m
C)6.0 × 10^-7 m
D)3.0 × 10^-7 m

Question 8

How far below the surface of water do you need to dive to double the atmospheric pressure? (Note: Atmospheric pressure is P_atm = 1.01 × 10⁵ Pa, and density of water is ñ = 1000 kg/m³.)

A)1 m
B)2 m
C)10 m
D)20 m

Question 9

A metal cube fully submerged in water shows an apparent weight of 1.9 N. When completely submerged in acetone, its apparent weight is 2.2 N. What is the length of the side of the cube? (Note: The density of water is ñ_water = 1000 kg/m³ and of acetone ñ_acetone = 784 kg/m³.)

A)5.0 × 10^-2 m
B)2.5 × 10^-3 m
C)1.4 × 10^-4 m
D)We need to know the mass of the cube to calculate the length.

Question 10

What unit is used to measure surface tension?

A)N m
B)Pa
C)kg/s²
D)kg m/s²

Question 11

A bucket of water has some ice floating in it. When water freezes into ice, the ice becomes less dense than water, and about 9% of ice volume is above the water. When the ice melts, what happens to the level of water in the bucket?

A)The level will go up 9%.
B)The level will go down 9%.
C)The level will go down more than 9%.
D)The level will remain the same.

Question 12

Figure 11.1
Dolphins are sleeping at the bottom of a cove, floating low above the ocean floor. Which diagram in Fig. 11.1 shows the correct forces acting on the dolphins?

A)diagram (a)
B)diagram (b)
C)diagram (c)
D)diagram (d)

Question 13

A 0.25 kg balloon is filled with helium. If the balloon is a sphere with a radius of 4 m, what is the maximum number of standard men it can lift? (Note: The density of air is ñ_air = 1.20 kg/m³ and of helium ñ_helium = 0.179 kg/m³; standard man has a mass of 70 kg.)

A)3 standard men
B)4 standard men
C)6 standard men
D)38 standard men

Question 14

In a glass of water, an olive sits atop a cube of ice. When the olive falls and sinks in the water, what happens to the level of water in the glass?

A)The level will go up.
B)The level will go down.
C)The level will remain the same.
D)We need to know the mass of the olive to answer.

Question 15

What would the perimeter of each foot have to be to enable a standard man (70 kg) to stand on the water on both feet, held up by surface tension? (Note: Surface tension for water ó = 0.073 N/m.)

A)9.3 × 10³ m
B)4.7 × 10³ m
C)9.6 × 10² m
D)4.8 × 10² m

Question 16

A piece of wood is floating on the water. Which one of these statements correctly describes buoyant force?

A)It is zero.
B)It is equal to the weight of the wood.
C)It is equal to all the other forces acting on the wood, but is opposite in direction.
D)It is equal in magnitude but opposite in direction to the weight of the wood.

Question 17

Which of these statements best describes the reason that fish can float in water?

A)The density of fish is higher than the density of water.
B)The weight of fish is higher than the weight of the same volume of water.
C)The density of fish is equal to the density of water.
D)The density of fish is lower than the density of water.

Question 18

A body is immersed in a fluid. Which of these statements correctly describes buoyant force?

A)It is equal to the weight of the object.
B)It is equal to the weight of the fluid displaced by the object.
C)It is equal to the pressure of water below the object.
D)It is equal to the mass of the fluid displaced by the object.

Question 19

What is the diameter of a capillary tube holding methanol, if the methanol rises to the same height as water in a 1 mm diameter tube? (Take 0° for contact angles, surface tension for water ó_H2O= 0.073 N/m, and of methanol ó_methanol = 0.023 N/m. Density of water is ñ_H2O = 1000 kg/m³, and of methanol ñ_methanol = 792 kg/m³.)

A)0.2 mm
B)0.4 mm
C)2.0 mm
D)4.0 mm

Question 20

You have a fluid in a beaker, but you need to increase the density of the contents of the beaker. How can you obtain higher density?

A)increase the fluid volume per unit mass
B)double the mass and volume of a fluid
C)halve the volume and mass of a fluid
D)increase the mass per unit volume

Question 21

Nautilus, a mollusk inside a spiral shell, sometimes dives as deep as 400 m below the ocean surface during the day in order to avoid heating by the sun. By what factor is the pressure exerted on the shell at that depth larger than the pressure at 60 m depth, where nautilus usually feeds on plankton? (Note: The density of sea water is ñ = 1030 kg/m³.)

Question 22

If no changes occur in a fluid, we say that it is in equilibrium. This statement includes all parameters of both macroscopic and microscopic motion of fluid molecules.

Question 23

Describe the position of a human body in which all the gauge pressures in the cardiovascular system are positive, and another position where you can expect negative gauge pressure to occur.

Question 24

At the surface of a fluid, the upward force from the fluid equals atmospheric pressure.

Question 25

Gauge pressure is the ratio of pressure to ambient (air) pressure.

Question 26

What is the apparent weight of an object immersed in a vessel filled with water, in a weightless environment, such as the International Space station?

Question 27

Surface tension is a force per unit area of the surface of a liquid.

Question 28

In a weightless environment such as on the International Space Station, water assumes the shape of a sphere.

Question 29

We can breathe in and out as long as the pressure between the outside and the inside of the lungs is lower than 0.05 times normal atmospheric pressure. How deep can we snorkel in sea water with density ñ = 1.025 × 10³ kg/m³, and in fresh water with density ñ = 1.0 × 10³ kg/m³?

Question 30

The ideal stationary fluid is incompressible. This means you cannot deform it. If you act on such a fluid to deform it, it responds with a change in density.

Question 31

Figure 11.2: A hydraulic lift
Hydraulic lift is shown in Fig. 11.2. The diameter of a large piston is 0.4 m. What is the diameter of a small piston if we can use a force of 147 N to lift a car of a mass 1500 kg?

Question 32

If the radius of a capillary tube decreases by 3 times, the water will rise to triple its original height.

Question 33

What percent of the weight of a ship's load has to be removed from a fully laden ship when it enters from the ocean into the St. Lawrence River? (Note: The density of sea water is ñ = 1.025 × 10³ kg/m³, and the density of fresh water is ñ = 10³ kg/m³.)

Question 34

If the height of a column of mercury supported by a blood pressure of 0.16 Pa is 120 mm, what height would a column of water be if you used a water manometer to measure the same pressure? (Note: The density of mercury is ñ = 1.36 × 10⁴ kg/m³, and the density of water is ñ = 10³ kg/m³.)

Question 35

Major cargo ships sail up the Saint Lawrence Seaway from the Atlantic Ocean to the Great Lakes. If their ballast tanks are not adjusted, the ships will sink lower when they move from the ocean to the fresh-water seaway.

Question 36

Buoyant force is sometimes directed upward and sometimes downward, depending on whether the object is sinking or floating.

Question 37

Use Pascal's law to determine the height of Earth's atmosphere. Compare the result to the height of Mount Everest, h = 8848 m. The real height of the atmosphere is about 500 km. What assumption in Pascal's law is the reason for this difference in results? (Note: Atmospheric pressure is P_atm = 1.01 × 10⁵ Pa, and density of air ñ = 1.2 kg/m³.)

Question 38

A shark has to swim constantly all its life to prevent its body from sinking because it is heavier than other types of fish.

Question 39

The density of ice is 917 kg/m³, and the density of sea water is 1025 kg/m³. A walrus climbs onto a piece of floating ice that has a volume of 15.7 m³. How much does the walrus weigh if the ice is just submerged under the surface of water?

Question 40

A body sinking in a fluid with terminal velocity has a weight equal to the buoyant force and the force of friction.

Question 41

Calculate the pressure in a water bubble of diameter 0.04 cm, and compare that with the pressure in the same diameter bubble of water-and-surfactant, which reduces surface tension by half. The surface tension of water is ó = 0.073 N/m.

Question 42

The fisher spider (Dolomedes triton), with mass of 0.7 g, walks on the water with eight legs. What length of each leg is in contact with the water so that the spider stays on the surface? Ignore the width of the leg; take into account only that each leg has two sides in contact with water. The surface tension of water is ó = 0.073 N/m.