Chapter 9 - The Behavior of Fluids

A gas initially is at a pressure of 75 kPa. If its volume is halved while the absolute temperature is kept constant the new pressure will be ___________ kPa.

150

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

A. 0.1 m.

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 4 m/s? A. 10.32 Pa. B. 2.58 Pa. C. 1.94 Pa. D. 1.29 Pa.

A. 10.32 Pa.

If the atmospheric pressure is 15 lb/in2 , what is the corresponding downward force on the top of a horizontal square area 6 inches on each side? A. 540 lbs. B. 90 lbs. C. 15 lbs. D. zero.

A. 540 lbs.

The glass in a window is 30 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. 88 pounds outward. B. 88 pounds inward. C. 8800 pounds outward. D. 8800 pounds inward. E. There would be no net force.

A. 88 pounds outward.

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

A. The pressure of the air in the tire increases.

. Imagine a steel pipe that doesn't leak from the sides and is 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 at 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.

A. The water pressure inside the tube rises at water is added.

If you sit in a boat on 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.

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

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

A. somewhat more than 10 pounds.

A child blows up a balloon with air. This balloon will not float to the ceiling because A. the balloon and the air it contains weigh more than the air displaced by the balloon. B. the weight of the balloon is less than the weight of the air displaced by the balloon. C. the pressure of the air inside the balloon is greater than the atmospheric pressure. D. the pressure of the air inside the balloon is less than the atmospheric pressure. E. the temperature of the air inside the balloon is less than the atmospheric temperature.

A. the balloon and the air it contains weigh more than the air displaced by the balloon.

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.

A. the man.

If you hold a light tissue in your hands and gently blow across its top, the tissue will rise slightly because A. the pressure of moving air is less than that of static air. B. collisions of the moving air with the tissue cause it to rise. C. blowing across the tissue removes all of the air, and then the air below the tissue pushes the tissue up. D. according to Archimedes' principle, moving air exerts more buoyant force.

A. the pressure of moving air is less than that of static air.

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

A. the red line is slightly higher than the water level.

The best shape for an automobile to have is one that is streamlined both in the front and the back. The reason for this is A. to ensure the air flow remains laminar all the way around the vehicle. 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 avoid uneven air flows that might push the vehicle sideways.

A. to ensure the air flow remains laminar all the way around the vehicle.

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

B. 20 kPa.

A hydraulic jack is used to lift a load of weight 5000 N. The load-bearing cylinder has a radius of 5 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. 200 N C. 1000 N D. 5000 N E. 25000 N

B. 200 N

. A hot air balloon derives its lift from the property of fluids as stated by A. Bernoulli's Principle. B. Archimedes' Principle. C. Boyle's Law. D. Pascal's Principle.

B. Archimedes' Principle.

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.

B. The elephant.

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.

B. The velocity over the wing is greater.

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.

B. a greater pressure can be applied with a sharp knife.

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

B. an object immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.

. A dump truck has a loosely tied canvas over its load. As the truck speeds down the highway, the canvas will tend to A. get pushed onto into the load. B. billow outward from the load. C. smooth out in a level, horizontal plane. D. lay limply in a jumbled pile.

B. billow outward from the load.

Suppose a little bubble of air has gotten into the top of mercury barometer. If a person uses a barometer in the usual way, the reading of atmospheric pressure will be A. correct. B. lower than the actual value. C. higher than the actual value.

B. lower than the actual value.

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

B. the balloon and the gas it contains weigh less than the air displaced by the balloon.

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

Bernoulli's Equation

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. Archimedes Principle. C. Boyle's Law. D. Pascal's Principle.

C. Boyle's Law.

Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius RA = 8 cm and flow velocity vA = 2 cm/s. Pipe B has radius RB = 4 cm and flow velocity vB = 4 cm/s. Compared to the rate of flow in pipe A, that in pipe B is A. the same. B. twice as large. C. half as large. D. depends on the length of the pipe.

C. half as large.

A penny, a quarter and a silver dollar 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. penny. B. quarter. C. silver dollar. D. All experience the same downward force.

C. silver dollar.

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 entirely submerged and then remain in place just below the surface. C. sink until it is almost, but not entirely submerged. 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.

C. sink until it is almost, but not entirely submerged.

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

C. snowshoes cover a larger area than a foot and so the pressure is reduced.

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

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

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

C. the red line is still at the water level.

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.

D. 9.1 N.

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.

D. Its density is close to but smaller than the density of water.

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.

D. The pressure in the straw is reduced and the liquid is pushed upward by atmospheric pressure on the

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

D. Viscosity

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

D. greater than when the cube was floating at the top.

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.

D. has sagged inward toward the coffee.

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 metric ton per hectare. C. one newton per square centimeter. D. one newton per square meter. E. None of these.

D. one newton per square meter.

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.

D. there is much less air above a mountain than above the oceans.

. 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 ______________.

Decrease

One section of a pipe carrying water has a cross-sectional area of 20 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 5 cm2 . If the flow is steady, what is the water velocity in the constricted section? A. 0.25 m/s B. 0.50 m/s C. 1.0 m/s D. 2.0 m/s E. 4.0 m/s

E. 4.0 m/s

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.

Greater Less

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.

Longer

A piece of soft wood floats in water with half of its volume submerged. If it is placed in alcohol which has a density 70% of that of water, it will float __________________ (higher, lower, same) compared with floating in water.

Lower

. The fact that an increase of pressure on an enclosed fluid is transmitted uniformly throughout the fluid is ______________ Law.

Pascal's

The operation of a hydraulic jack is based upon _______________ Law.

Pascal's

When the flow of air is ___________, more drag is created on objects moving through the fluid.

Turbulent

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

Viscosity