Deck 9: The Behavior of Fluids

Question 1

If you sit in a boat near the edge of a river channel, you might notice the water moving more quickly on the side away from the shore (the channel side). If you are initially moving with the river, you will be pushed

A) into the channel because the water pressure is larger on the shore side.
B) into the channel by the turbulent flow of the water.
C) toward the shore because the water flow is laminar around the boat.
D) toward the shore because the water pressure is smaller on the shore side.

Answer 1

into the channel because the water pressure is larger on the shore side.

Question 2

A boat floating in a large pool is loaded with wood blocks. The water level at the pool's edge is marked with a red line. The blocks are now thrown overboard and float outside the boat. When the water becomes calm again,

A) the red line is slightly lower than the water level.
B) the red line is slightly higher than the water level.
C) the red line is still at the water level.

Answer 2

the red line is still at the water level.

Question 3

The skinny tires of a 10-speed racing bicycle require more air pressure than the fat tires on an equally massive mountain bike because

A) the racing bike moves faster.
B) the racing bike touches the ground over a smaller area than the bike with fat tires.
C) the area of contact of the racing bike's tires is greater than that of the bike with fat tires.
D) the racing bike exerts more force on the ground.

Answer 3

the racing bike touches the ground over a smaller area than the bike with fat tires.

Question 4

A child is drinking a liquid with a straw. Which of the following statements is true?

A) The fluid is being pulled up into the straw.
B) Longer straws work better because the pressure is larger deeper down.
C) The pressure inside the straw depends on the viscosity of the liquid.
D) The pressure in the straw is reduced and the liquid is pushed upward by atmospheric pressure on the surface of the liquid.

Question 5

One morning you discover that a tire on your auto is in need of air. As you add air to the tire, which of the following statements is true?

A) The density of the air in the tire gets smaller.
B) The pressure of the air in the tire increases.
C) The number of atoms of air in the tire stays the same.
D) All of the statements are true.

Question 6

Three individuals stand with all of their weight on the heel of one foot: a man of weight 600 N and a heel area of 100 cm², a child of weight 200 N and a heel area of 25 cm², and woman of weight 450 N and a heel area of 2 cm². The one exerting the least pressure on the ground is

A) the man.
B) the child.
C) the woman.
D) All exert the same.

Question 7

If you hold a light tissue in your hands and gently blow across its top, the tissue will rise slightly because

A) blowing across the tissue removes all of the air, and then the air below the tissue pushes the tissue up.
B) collisions of the moving air with the tissue cause it to rise.
C) the pressure of moving air is less than that of static air.
D) according to Archimedes' Principle, moving air exerts more buoyant force.

Question 8

Hot coffee is poured into a cylindrical container until it is nearly full. The container is immediately sealed by stretching a rubber balloon across the container mouth and tightly sealing the edges. Twenty minutes later, you observe that the still intact rubber seal

A) has bulged outward in the center of the mouth of the container.
B) is still flat across the entire mouth of the container.
C) has bulged outward only at the edges of the container mouth.
D) has sagged inward toward the coffee.

Question 9

A silver dollar, a quarter, and a penny(these are in order of decreasing diameter) lie at the bottom of a wishing well filled with water. The coin experiencing the largest downward force on its top surface due to the water pressure is the

A) silver dollar.
B) quarter.
C) penny.
D) All experience the same downward force.

Question 10

A clown at the circus blows up a balloon with helium. This balloon will not float to the ceiling unless

A) the pressure of the helium inside the balloon is greater than the atmospheric pressure.
B) the weight of the balloon is less than the weight of the air displaced by the balloon.
C) the balloon and the helium it contains weigh less than the air displaced by the balloon.
D) the pressure of the helium inside the balloon is less than the atmospheric pressure.

Question 11

An ice cube in a glass of water is pushed to the bottom of the glass and held there with a straw. Consequently, the buoyant force on the ice cube is now

A) exactly balanced by the force exerted only by the straw.
B) exactly balanced by the weight of the ice cube.
C) greater than when the cube was floating at the top.
D) the same as when the cube was floating at the top.

Question 12

A boat floating in a large pool is loaded with solid iron bars. The water level at the pool's edge is marked with a red line. The iron is now thrown overboard. When the water becomes calm again,

A) the red line is slightly lower than the water level.
B) the red line is slightly higher than the water level.
C) the red line is still at the water level.

Question 13

An iceberg is floating in the ocean with 10% of its volume extending above the ocean's surface. What can you say about the iceberg?

A) Its weight is less than the water it displaces.
B) It displaces only 90% of its weight in water.
C) As it melts, a smaller fraction of its volume will extend above the surface.
D) Its density is close to but smaller than the density of water.

Question 14

If the atmospheric pressure is 15 lb/in², what is the corresponding downward force on the top of a horizontal square area 5 inches on each side?

A) zero.
B) 15 lbs.
C) 75 lbs.
D) 375 lbs.

Question 15

It is observed that, as bubbles rise in a deep column of water, the diameter of the bubbles increases. This is best explained by

A) Bernoulli's Principle.
B) Boyle's Law.
C) Archimedes' Principle.
D) Pascal's Principle.

Question 16

Archimedes' Principle states that...

A) an object immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.
B) the pressure of a fluid is inversely proportional to the temperature of the fluid.
C) the pressure in a fluid is directly related to the depth below the surface of the fluid.
D) the velocity of a fluid is directly proportional to the pressure exerted on the fluid.

Question 17

A sharp knife can more easily cut objects than can a dull knife because

A) a greater force can be applied with a sharp knife.
B) a greater pressure can be applied with a sharp knife.
C) dull knives cannot apply large forces.
D) sharp knives have edges that can fit between the molecules of the object.

Question 18

A hot air balloon derives its lift from the property of fluids as stated by

A) Bernoulli's Principle.
B) Boyle's Law.
C) Pascal's Principle.
D) Archimedes' Principle.

Question 19

An ant and an elephant are walking through the jungle. On which does the greater buoyant force act?

A) The ant.
B) The elephant.
C) The same buoyant force acts on both.
D) Neither is floating, so no buoyant force is acting at all.

Question 20

A balloon inflated with helium is able to float toward the ceiling because

A) the weight of the balloon is greater than the weight of the air displaced by the balloon.
B) the density of the gas inside the balloon is greater than the density of the atmosphere.
C) the pressure of the gas inside the balloon is less than the atmospheric pressure.
D) the pressure of the gas inside the balloon is greater than the atmospheric pressure.
E) the balloon and the gas it contains weigh less than the air displaced by the balloon.

Question 21

A dump truck has a loosely tied canvas over its empty bed, which is full of still air. As the truck speeds down the highway, the canvas will tend to

A) get pushed onto the load.
B) billow outward from the load.
C) smooth out in a level, horizontal plane.
D) lay limply in a jumbled pile.

Question 22

A uniform wooden plank floats in a swimming pool. The plank weighs 100 pounds, and exactly 10% of its volume is above the waterline. The maximum weight of iron which could be suspended from underneath the plank without causing the whole combination to sink to the bottom of the pool is

A) exactly 10 pounds.
B) somewhat more than 10 pounds.
C) somewhat less than 10 pounds.
D) more information is needed.

Question 23

One section of a pipe carrying water has a cross-sectional area of 16 cm²; in this section the water has flow velocity of 1.0 m/s. Another section of this pipe has a constricted cross-sectional area of 4 cm². If the flow is steady, what is the water velocity in the constricted section?

A) 4.0 m/s
B) 2.0 m/s
C) 1.0 m/s
D) 0.50 m/s
E) 0.25 m/s

Question 24

A gas originally occupies a volume of 0.5 m³ at a pressure of 100 kPa. It is slowly allowed to expand until the volume is 2.5 m³. Assuming the temperature is kept constant, the final pressure will be

A) 500 kPa.
B) 100 kPa.
C) 50 kPa.
D) 20 kPa.
E) 10 kPa.

Question 25

A person wearing snowshoes can walk across a blanket of freshly fallen snow without sinking far into the snow because

A) the snowshoes reduce the force of the person on the snow.
B) the large area of the snowshoe concentrates the force of the person to a point smaller than the foot.
C) snowshoes cover a larger area than a foot and so the pressure is reduced.
D) snowshoes push less dense snow out of the way so the person stands on more solid ice below.

Question 26

In U.S. customary units, air pressure is measured in pounds per square inch. In the metric system, it is measured in Pascals, and one Pascal is equal to

A) one pound per square foot.
B) one newton per square meter.
C) one newton per square centimeter.
D) one metric ton per hectare.
E) none of these.

Question 27

Suppose a little bubble of air has gotten into the top of a mercury barometer. If a person uses a barometer in the usual way, the reading of atmospheric pressure will be

A) correct.
B) higher than the actual value.
C) lower than the actual value.

Question 28

The glass in a window is 35 inches wide and 20 inches tall, and standard atmospheric pressure is 14.7 pounds per square inch. What net force would result on the glass if the air pressure outside the house were 1% lower than the air pressure inside?

A) 103 pounds inward.
B) 103 pounds outward.
C) 10300 pounds inward.
D) 10300 pounds outward.
E) There would be no net force.

Question 29

One morning you discover that a tire on your auto is in need of air. This is visible: it has flattened significantly. Significant flattening indicates low air pressure

A) only if all tires are equally flattened; otherwise it is just low atmospheric pressure.
B) because more of the tire's surface area is required to provide same amount of force.
C) and less weight.
D) and higher temperature.

Question 30

The density of aluminum is 2700 kg/m³. An aluminum block has a mass of 2.5 kg. The buoyant force exerted on this block when it is completely submerged in water of density 1000 kg/m³ is approximately

A) 0.0091 N.
B) 0.93 N.
C) 2.5 N.
D) 9.1 N.
E) 24.5 N.

Question 31

Imagine a steel pipe that doesn't leak from the sides and is already filled with water. Water enters at a rate of 2 kg/s but leaves at a rate of 1 kg/s. Which of the following is true?

A) The water pressure inside the tube rises as water is added.
B) The tube is narrower where the water enters than where it leaves.
C) The water flow must be laminar.
D) It is not possible for this situation to occur.

Question 32

The density of ice is about 900 kg/m³, and the density of water is about 1000 kg/m³. A cubic block of ice one meter on a side floats in water. Assuming that the lowest square face of the cube is horizontal, the height of the block above the water line is

A) 0.9 m.
B) 0.8 m.
C) 0.5 m.
D) 0.2 m.
E) 0.1 m.

Question 33

The best shape for an automobile to have is one that is streamlined both in the front and in the back. The reason for this is

A) to avoid uneven air flows that might push the vehicle sideways.
B) to improve fuel efficiency when driving in reverse.
C) to use the viscosity of the air to help propel the automobile forward.
D) to ensure the air flow remains laminar all the way around the vehicle.

Question 34

A hydraulic jack is used to lift a load of weight 4000 N. The load-bearing cylinder has a radius of 4 cm, and the other piston has a radius of 1 cm. What force must be exerted on the smaller piston to support the load?

A) 100 N
B) 250 N
C) 1000 N
D) 4000 N
E) 16,000 N

Question 35

Atmospheric pressure decreases as one moves to higher elevations because

A) the force of gravity is weaker on a mountain than at sea level.
B) it is much colder on a mountain than at sea level.
C) the air moves at higher speeds near mountains than over the oceans.
D) there is much less air above a mountain than above the oceans.

Question 36

How does the velocity of air moving over the top of the wing of an airplane in flight compare to the velocity of air moving under the wing?

A) The velocities are the same.
B) The velocity over the wing is greater.
C) The velocity under the wing is greater.

Question 37

A block that has a density of 900 kg/m³ is placed in water (density 1000 kg/m³). The block will

A) sink to the bottom.
B) sink until it is almost, but not entirely, submerged.
C) sink until it is entirely submerged and then remain in place just below the surface.
D) sink just a little bit with most of the block above the water.
E) rest on the water with none of the block submerged.

Question 38

Some people say that, based on the arrangement of its molecules, glass should be considered a liquid. If we think of glass as a liquid, in which of these properties is it most unlike other common liquids?

A) Weight
B) Density
C) Transparency
D) Viscosity

Question 39

According to Bernoulli's equation, the pressure in a fluid will tend to decrease if its velocity increases. Assuming that a wind speed of 1 m/s causes a pressure drop of 0.645 Pa, what pressure drop is predicted by Bernoulli's equation for a wind speed of 5 m/s?

A) 1.29 Pa
B) 1.94 Pa
C) 3.325 Pa
D) 16.125 Pa

Question 40

Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius R_A = 8 cm and flow velocity v_A = 2 cm/s. Pipe B has radius R_B = 4 cm and flow velocity v_B = 4 cm/s. Compared to the rate of flow in pipe A, that in pipe B is

A) the same.
B) half as large.
C) twice as large.
D) It depends on the length of the pipe.

Question 41

Aerodynamic lift results from ___________ Principle.

Question 42

Pascal's Principle states that an increase of pressure on an enclosed fluid is transmitted _________ throughout the fluid.

Question 43

When the flow of air over an object is laminar, ________ drag is created on the object.

Question 44

A baseball pitcher throws a curveball, and Bernoulli's Principle gives a fair description of why it takes such a drastic curve. If that pitcher could throw the exact same pitch on the Moon, then

A) it would curve more drastically, because gravity is so much weaker on the Moon.
B) it would curve more drastically, because there is no counterforce from air pressure on the Moon.
C) it would curve but not as much as on Earth, since the Moon's gravity is so weak.
D) it would not curve at all, because the Moon has no atmosphere.

Question 45

Storm winds blowing at high speed over a roof can destroy the roof of a closed-up house because of Bernoulli's Principle. What happens is

A) the roof is pushed inward and collapses.
B) the wind inside the house blows out the roof from the inside.
C) the higher pressure inside lifts the roof off the walls.
D) friction rips up the roof and blows it apart.

Question 46

Which of the following statements is true?

A) A floating ocean liner will displace its own volume of water.
B) A submerged submarine will displace its own volume of water.
C) A floating ocean liner will displace its own weight of water.
D) None of the above statements are true.

Question 47

If a barometer were to be made using water as the liquid instead of mercury, the length of the barometer tube for water would be _________________ than the tube for a standard mercury barometer.

Question 48

The carburetor of a car is a pipe with a constriction. Compared to the velocity of flow of a mixture of air and gasoline in the main pipe, the velocity in the constriction will be ______. The pressure in the constriction will be ___________ than the pressure in the main pipe.

Question 49

Other things (density, altitude, temperature) being equal, a moving gas exerts less pressure than a stationary gas. This is predicted by _______________________ (2 words).

Question 50

The operation of hydraulic brakes in a car is based upon _______________ Principle.

Question 51

Suppose you have 10 helium-filled party balloons tied to a digital camera, so you can take photos of the core of a storm. With 10 balloons the camera will slowly but surely rise. As a storm approaches the atmospheric pressure drops. Assuming the air temperature and density are the same, the volume of each balloon will increase. When you let go, the speed of ascent will be _____________.

Question 52

A piece of soft wood floats in water with half of its volume submerged. If it is placed in mercury which has a density about 13.6 times that of water, it will float __________________ (higher, lower, the same) compared with floating in water.

Question 53

A fluid that flows very slowly compared to water has a high ____________.

Question 54

Suppose you have a helium-filled weather balloon above the house. As a storm leaves, the atmospheric pressure rises. Assuming the air temperature is the same, the volume of the balloon will ______________.

Question 55

A sealed hot air balloon is capable of rising to high altitudes when it is initially released. As the air in the balloon cools, however, it eventually comes back down to the ground because

A) what goes up must come down.
B) objects heavier than air can only fly through the air with the help of a motor.
C) the object comes down when the air in it eventually leaks out.
D) objects can only float in a fluid if their density is less than that of the fluid.
Fill in the Blank Questions

Question 56

Even though your car weighs several thousand pounds, it can easily be raised above your head by a pneumatic lift at the service station by a small motor pumping fluid through a pipe. This an illustration of

A) Pascal's Principle.
B) Archimedes' Principle.
C) Bernoulli's Law.
D) Newton's 3^rd Law.

Question 57

A gas initially is at a pressure of 35 kPa. If its volume is halved while the absolute temperature is kept constant the new pressure will be ___________ kPa.