Deck 14: Fluids

Question 1

All fluids are:

A) gases
B) liquids
C) gases or liquids
D) non-metallic
E) transparent

Answer 1

gases or liquids

Question 2

A bucket resting on the floor of an elevator contains an incompressible fluid of density $\rho$ . When the elevator has an upward acceleration a the pressure difference between two points in a fluid separated by a vertical distance $\Delta$ h, is given by:

A) $\rho$ a $\Delta$ h
B) $\rho$ g $\Delta$ h
C) $\rho$ (g + a) $\Delta$ h
D) $\rho$ (g - a) $\Delta$ h
E) $\rho$ ga $\Delta$ h

Answer 2

$\rho$ (g + a) $\Delta$ h

Question 3

Several cans of different sizes and shapes are all filled with the same liquid to the same depth. Then:

A) the weight of the liquid is the same for all cans
B) the force of the liquid on the bottom of each can is the same
C) the least pressure is at the bottom of the can with the largest bottom area
D) the greatest pressure is at the bottom of the can with the largest bottom area
E) the pressure on the bottom of each can is the same

Answer 3

the pressure on the bottom of each can is the same

Question 4

A bucket of water is pushed from left to right with increasing speed across a horizontal surface. Consider the pressure at two points at the same level in the water.

A) It is the same
B) It is higher at the point on the left
C) It is higher at the point on the right
D) At first it is higher at the point on the left but as the bucket speeds up it is lower there
E) At first it is higher at the point on the right but as the bucket speeds up it is lower there

Question 5

1 Pa is:

A) 1 N/m
B) 1 m/N
C) 1 kg/m.s
D) 1 kg/m.s²
E) 1 N/m.s

Question 6

Gases may be distinguished from other forms of matter by their:

A) lack of color
B) small atomic weights
C) inability to form free surfaces
D) ability to flow
E) ability to exert a buoyant force

Question 7

A bucket resting on the floor of an elevator contains an incompressible fluid of density $\rho$ . When the elevator has a downward acceleration of magnitude a the pressure difference between two points in a fluid, separated by a vertical distance $\Delta$ h, is given by:

A) $\rho$ a $\Delta$ h
B) $\rho$ g $\Delta$ h
C) $\rho$ (g + a) $\Delta$ h
D) $\rho$ (g - a) $\Delta$ h
E) $\rho$ ga $\Delta$ h

Question 8

Which of the following five statements, concerning the upper surface pressure of a liquid, is FALSE?

A) it is independent of the surface area
B) it is the same for all points on that surface
C) it would not increase if the liquid depth were increased
D) it would increase if the liquid density were increased
E) it would increase if the atmospheric pressure increased

Question 9

A uniform U-tube is partially filled with water. Oil, of density 0.75 g/cm³, is poured into the right arm until the water level in the left arm rises 3 cm. The length of the oil column is then:

A) 2.25 cm
B) 8 cm
C) 6 cm
D) 4 cm
E) need to know the cross-sectional area of the U-tube

Question 10

In a stationary homogeneous liquid:

A) pressure is the same at all points
B) pressure depends on the direction
C) pressure is independent of any atmospheric pressure on the upper surface of the liquid
D) pressure is the same at all points at the same level
E) none of the above

Question 11

The density of water is 1.0 g/cm³. If h = 20 cm, the density of the oil in the left column of the U-tube shown below is:

A) 0.20 g/cm³
B) 0.90 g/cm³
C) 1.0 g/cm³
D) 1.3 g/cm³
E) 5.0 g/cm³

Question 12

To obtain the absolute pressure from the gauge pressure:

A) subtract atmospheric pressure
B) add atmospheric pressure
C) subtract 273
D) add 273
E) convert to N/m²

Question 13

Mercury is a convenient liquid to use in a barometer because:

A) it is a metal
B) it has a high boiling point
C) it expands little with temperature
D) it has a high density
E) it looks silvery

Question 14

A long U-tube contains mercury (density = 14 * 10³ kg/m³). When 10 cm of water (density = 1.0 *10³ kg/m ³) is poured into the left arm, the mercury in the right arm rises above its original level by:

A) 0.36 cm
B) 0.72 cm
C) 14 cm
D) 35 cm
E) 70 cm

Question 15

If p is a pressure and $\rho$ is a mass density then p/ $\rho$ has units of:

A) m²
B) m²/s²
C) N/m²
D) kg/m²
E) m³/kg

Question 16

A closed hemispherical shell of radius R is filled with fluid at uniform pressure p. The net force of the fluid on the curved portion of the shell is given by:

A) 2 $\pi$ R²p
B) $\pi$ R²p
C) 4 $\pi$ R²p
D) (4/3) $\pi$ R²p
E) (4/3) $\pi$ R³p

Question 17

The vessels shown below all contain water to the same height. Rank them according to the pressure exerted by the water on the vessel bottoms, least to greatest.

A) 1, 2, 3, 4
B) 3, 4, 2, 1
C) 1, 2, 4, 3
D) 2, 3, 4, 1
E) All pressures are the same

Question 18

The pressure exerted on the ground by a man is greatest when:

A) he stands with both feet flat on the ground
B) he stands flat on one foot
C) he stands on the toes of one foot
D) he lies down on the ground
E) all of the above yield the same pressure

Question 19

The diagram shows a U-tube having cross-sectional area A and partially filled with oil of density $\rho$ . A solid cylinder, which fits the tube tightly but can slide without friction, is placed in the right arm. The system reaches equilibrium. The weight of the cylinder is:

A) AL $\rho$ g
B) L³ $\rho$ g
C) A $\rho$ (L + h)g
D) A $\rho$ (L - h)g
E) none of these

Question 20

An airtight box, having a lid of area 80.0 cm², is partially evacuated. Atmospheric pressure is 1.01 * 10⁵ Pa. A force of 108 lb is required to pull the lid off the box. The pressure in the box was:

A) 1.35 * 10⁴ Pa
B) 2.60 *10⁴ Pa
C) 4.10 * 10⁴ Pa
D) 8.75 *10⁴ Pa
E) 1.36 *10⁵ Pa

Question 21

A cork floats on the surface of an incompressible liquid in a container exposed to atmospheric pressure. The container is then sealed and the air above the liquid is evacuated. The cork:

A) sinks slightly
B) rises slightly
C) floats at the same height
D) bobs up and down about its old position
E) behaves erratically

Question 22

A block of ice at 0 $\degree$ C containing a piece of cork is floating on the surface of water in a beaker. When the ice has melted the water level:

A) is higher
B) is lower
C) is the same
D) depends on the initial ratio of water to ice
E) depends on the shape of the ice block

Question 23

A U-tube has dissimilar arms, one having twice the diameter of the other. It contains an incompressible fluid and is fitted with a sliding piston in each arm, with each piston in contact with the fluid. When an applied force does work W in pushing the piston in the narrow arm down, the fluid does work __________ on the piston in the wide arm.

A) W
B) 2W
C) W/2
D) 4W
E) W/4

Question 24

A small steel ball floats in a half-full container of mercury. When water is added:

A) the ball will float on the water
B) the ball will rise slightly
C) the mercury will float on the water
D) the ball will sink to the bottom of the container
E) the ball will lower slightly more into the mercury

Question 25

Two identical blocks of ice float in water as shown. Then:

A) block A displaces a greater volume of water since the pressure acts on a smaller bottom area
B) block B displaces a greater volume of water since the pressure is less on its bottom
C) the two blocks displace equal volumes of water since they have the same weight
D) block A displaces a greater volume of water since its submerged end is lower in the water
E) block B displaces a greater volume of water since its submerged end has a greater area

Question 26

"An object completely submerged in a fluid displaces its own volume of fluid." This is:

A) Pascal's paradox
B) Archimedes' principle
C) Pascal's principle
D) true, but none of the above
E) false

Question 27

A pirate chest rests at the bottom of an ocean. If the water is still, the net force it exerts on the chest:

A) is upward
B) is downward
C) is zero
D) depends on the mass of the chest
E) depends on the contents of the chest

Question 28

The two arms of a U-tube are not identical, one having twice the diameter of the other. A cork in the narrow arm requires a force of 16 N to remove it. The tube is filled with water and the wide arm is fitted with a piston. The minimum force that must be applied to the piston to push the cork out is:

A) 4 N
B) 8 N
C) 16 N
D) 32 N
E) 64 N

Question 29

A block of wood weighs 160 N and has a specific gravity of 0.60. To sink it in fresh water requires an additional downward force of:

A) 54 N
B) 64 N
C) 96 N
D) 110 N
E) 240 N

Question 30

Barometers and open-tube manometers are two instruments that are used to measure pressure. Which statement is true?

A) Both measure gauge pressure
B) Both measure absolute pressure
C) Barometers measure gauge pressure and manometers measure absolute pressure
D) Barometers measure absolute pressure and manometers measure gauge pressure
E) Both measure an average of the absolute and gauge pressures

Question 31

To measure moderately low pressures oil with a density of 8.5 * 10² kg/m³ is used in place of mercury in a barometer. A change in the oil column of 1.0 mm indicates a change in pressure of about:

A) 1.2 *10^-7 Pa
B) 1.2 *10^-5 Pa
C) 0.85 Pa
D) 1.2 Pa
E) 8.3 Pa

Question 32

A block of ice at 0 $\degree$ C is floating on the surface of water in a beaker. The surface of the water just comes to the top of the beaker. When the ice melts the water level will:

A) rise and overflow will occur
B) remain the same
C) fall
D) depend on the initial ratio of water to ice
E) depend on the shape of the block of ice

Question 33

An open-tube manometer is used to measure the gauge pressure in a tank. If the manometer is filled with mercury, and the open end is at a height of 15 cm above the end attached to the tank, what is the gauge pressure in the tank? The density of mercury is 14 x 10³ kg/m³.

A) 2.1 x 10³ Pa
B) 2.1 x 10⁴ Pa
C) 4.0 x 10⁴ Pa
D) 1.2 x 10⁵ Pa
E) 2.1 x 10⁶ Pa

Question 34

A U-tube has dissimilar arms, one having twice the diameter of the other. It contains an incompressible fluid and is fitted with a sliding piston in each arm, with each piston in contact with the fluid. When the piston in the narrow arm is pushed down a distance d, the piston in the wide arm rises a distance:

A) d
B) 2d
C) d/2
D) 4d
E) d/4

Question 35

One piston in a hydraulic lift has an area that is twice the area of the other. When the pressure at the smaller piston is increased by $\Delta$ p the pressure at the larger piston:

A) increases by 2 $\Delta$ p
B) increases by $\Delta$ p/2
C) increases by $\Delta$ p
D) increases by 4 $\Delta$ p
E) does not change

Question 36

A certain object floats in fluids of density Which of the following statements is true?

A) the buoyant force of fluid 1 is greater than the buoyant forces of the other two fluids
B) the buoyant force of fluid 3 is greater than the buoyant forces of the other two fluids
C) the three fluids exert the same buoyant force
D) the object displace the same volume of all three fluids
E) none of these are true

Question 37

A hydraulic press has one piston of diameter 2.0 cm and the other piston of diameter 8.0 cm. What force must be applied to the smaller piston to obtain a force of 1600 N at the larger piston:

A) 100 N
B) 400 N
C) 1600 N
D) 6400 N
E) 26000 N

Question 38

The principle of fluid pressure which is used in hydraulic brakes or lifts is that:

A) pressure is the same at all levels in a fluid
B) increases of pressure are transmitted equally to all parts of a fluid
C) the pressure at a point in a fluid is due to the weight of the fluid above it
D) increases of pressure can only be transmitted through fluids
E) the pressure at a given depth is proportional to the depth in the fluid

Question 39

Which of the following statements about Pascal's principle is true?

A) It is valid only for incompressible fluids
B) It explains why light objects float
C) It explains why the pressure is greater at the bottom of a lake than at the surface
D) It is valid only for objects that are less dense than water
E) None of the above is true

Question 40

The hydraulic automobile jack illustrates:

A) Archimedes' principle
B) Pascal's principle
C) Hooke's law
D) Newton's third law
E) Newton's second law

Question 41

An object floats on the surface of a fluid. For purposes of calculating the torque on it, the buoyant force is taken to act at:

A) the center of the bottom surface of the object
B) the center of gravity of the object
C) the center of gravity of the fluid that the object replaced
D) the geometric center of the object
E) none of the above

Question 42

A student standardizes the concentration of a salt-water solution by slowly adding salt until an egg will just float. The procedure is based on the assumption that:

A) all eggs have the same volume
B) all eggs have the same weight
C) all eggs have the same density
D) all eggs have the same shape
E) the salt tends to neutralize the cholesterol in the egg

Question 43

A tin can has a volume of 1000 cm³ and a mass of 100 g. Approximately what mass of lead shot can it carry without sinking in water?

A) 900 g
B) 100 g
C) 1000 g
D) 1100 g
E) 980 g

Question 44

A 210-g object apparently loses 30 g when suspended in a liquid of density 2.0 g/cm³. The density of the object is:

A) 7.0 g/cm³
B) 3.5 g/cm³
C) 1.4 g/cm³
D) 14 g/cm³
E) none of these

Question 45

A fluid is undergoing "incompressible" flow. This means that:

A) the pressure at a given point cannot change with time
B) the velocity at a given point cannot change with time
C) the velocity must be the same everywhere
D) the pressure must be the same everywhere
E) the density cannot change with time or location

Question 46

An object hangs from a spring balance. The balance indicates 30 N in air, 20 N when the object is submerged in water. What does the balance indicate when the object is submerged in liquid with a density that is half of water?

A) 20 N
B) 25 N
C) 30 N
D) 35 N
E) 40 N

Question 47

A wood board floats in fresh water with 60% of its volume under water. The density of the wood is:

A) 0.4 g/cm³
B) 0.5 g/cm³
C) 0.6 g/cm³
D) less than 0.4 g/cm³
E) more than 0.6 g/cm³

Question 48

A rock, which weighs 1400 N in air, has an apparent weight of 900 N when submerged in fresh water (998 kg/m³). The volume of the rock is:

A) 0.14 m³
B) 0.50 m³
C) 0.90 m³
D) 5.1 *10^-2 m³
E) 9.2 *10^-2 m³

Question 49

A 0.50 N metal sinker appears (as measured using a spring scale) to have a mass of 0.45 N when submerged in water. The specific gravity of the metal is:

A) 6
B) 8
C) 9
D) 10
E) 12

Question 50

An object hangs from a spring balance. The balance indicates 30 N in air, 20 N when the object is submerged in water. Which of the following is true?

A) The actual weight of the object is 20 N.
B) The actual weight of the object is 10 N.
C) The actual weight of the object is slightly more than 30 N, due to the buoyant force of the air.
D) The actual weight of the object is slightly less than 30 N, due to the buoyant force of the air.
E) The actual weight of the object is equal to the apparent weight of the object in both cases.

Question 51

A loaded ship passes from a lake (fresh water) to the ocean (salt water). Salt water is denser than fresh water and as a result the ship will:

A) ride higher in the water
B) settle lower in the water
C) ride at the same level in the water
D) experience an increase in buoyant force
E) experience a decrease in buoyant force

Question 52

A boat floating in fresh water displaces 16,000 N of water. How many newtons of salt water would it displace if it floats in salt water of specific gravity 1.10?

A) 12,800 N
B) 14,400 N
C) 16,000 N
D) 17,600 N
E) 19,200 N

Question 53

The dimensions of a wooden raft (density = 150 kg/m³) are 3.0 m * 3.0 m * 1.0 m. What maximum load can it carry in sea water (density =1020 kg/m³)?

A) 1350 kg
B) 7800 kg
C) 9200 kg
D) 19,500 kg
E) 24,300 kg

Question 54

A solid has a volume of 8 cm³. When weighed on a spring scale calibrated in grams, the scale indicates 20 g. What does the scale indicate if the object is weighed while immersed in a liquid of density 2 g/cm³?

A) 4 g
B) 10 g
C) 12 g
D) 16 g
E) zero, since the object will float

Question 55

The apparent weight of a steel sphere immersed in various liquids is measured using a spring scale. The greatest reading is obtained for that liquid:

A) having the smallest density
B) having the largest density
C) subject to the greatest atmospheric pressure
D) having the greatest volume
E) in which the sphere was submerged deepest

Question 56

Two balls have the same shape and size but one is denser than the other. When they are dropped in air, which has the greater acceleration? Do not ignore air resistance.

A) The heavier ball
B) The lighter ball
C) They have the same acceleration
D) The heavier ball if atmospheric pressure is high, they lighter ball if it is low
E) The lighter ball if atmospheric pressure is high, the heavier ball if it is low

Question 57

A blast of wind tips a sailboat in the clockwise direction when viewed from the stern. When the wind ceases the boat rotates back toward the upright position if, when it is tilted, the center of buoyancy:

A) is above the center of gravity
B) is below the center of gravity
C) is to the right of the center of gravity
D) is to the left of the center of gravity
E) coincides with the center of gravity

Question 58

The equation of continuity for fluid flow can be derived from the conservation of:

A) energy
B) mass
C) angular momentum
D) volume
E) pressure

Question 59

A cork floats in water in a bucket resting on the floor of an elevator. The elevator then accelerates upward. During the acceleration:

A) the cork is immersed more
B) the cork is immersed less
C) the cork is immersed the same amount
D) at first the cork is immersed less but as the elevator speeds up it is immersed more
E) at first the cork is immersed more but as the elevator speeds up it is immersed less

Question 60

A steel ax and an aluminum piston have the same apparent weight in water. When they are weighed in air:

A) they weigh the same
B) the ax is heavier
C) the piston is heavier
D) both weigh less than they did in water
E) depends on their shapes

Question 61

The units of pressure can also be written as:

A) N/m
B) J∙m²
C) W/m²
D) J/m³
E) N/m³

Question 62

Water flows from a 6.0-cm diameter pipe into an 8.0-cm diameter pipe. The speed in the 6.0-cm pipe is 5.0 m/s. The speed in the 8-inch pipe is:

A) 2.8 m/s
B) 3.8 m/s
C) 6.7 m/s
D) 8.9 m/s
E) 9.9 m/s

Question 63

The diagram shows a pipe of uniform cross section in which water is flowing. The directions of flow and the volume flow rates (in cm³/s) are shown for various portions of the pipe. The direction of flow and the volume flow rate in the portion marked A are:

A) $\downarrow$ and 3 cm³/s
B) $\uparrow$ and 7 cm³/s
C) $\downarrow$ and 9 cm³/s
D) $\uparrow$ and 11 cm³/s
E) $\downarrow$ and 15 cm³/s

Question 64

A water line enters a house 2.0 m below ground. A smaller diameter pipe carries water to a faucet 5.0 m above ground, on the second floor. Water flows at 2.0 m/s in the main line and at 7.0 m/s on the second floor. Take the density of water to be 1.0 * 10³ kg/m³. The pressure in the main line is 2.0 *10⁵ Pa; then the difference in pressure between the main line and the second floor is:

A) 6.9 *10⁴ Pa with the main line at the higher pressure
B) 2.3 *10⁴ Pa with the main line at the higher pressure
C) 6.9 *10⁴ Pa with the main line at the lower pressure
D) 2.3 * 10⁴ Pa with the main line at the lower pressure
E) 9.1 *10⁴ Pa with the main line at the higher pressure

Question 65

Water is streaming downward from a faucet opening with an area of 3.0 *10^-5 m². It leaves the faucet with a speed of 5.0 m/s. The cross sectional area of the stream 0.50 m below the faucet is:

A) 1.5 * 10^-5 m²
B) 2.0 * 10^-5 m²
C) 2.5* 10^-5 m²
D) 3.0 * 10^-5 m²
E) 3.5 *10^-5 m²

Question 66

Water (density = 1.0 * 10³ kg/m³) flows downhill through a pipe of diameter 1.5 cm. Its speed at the top of the hill is 7.2 m/s. If the hill is 9.5 m high, what is the gravitational potential energy density of the water at the top of the hill relative to the bottom?

A) cannot be calculated without knowing the pressure
B) 120 J/m³
C) 7.2 x 10³ J/m³
D) 9.5 x 10³ J/m³
E) 9.3 x 10⁴ J/m³

Question 67

Water flows through a cylindrical pipe of varying cross-section. The velocity is 3.0 m/s at a point where the pipe diameter is 1.0 cm. At a point where the pipe diameter is 3.0 cm, the velocity is:

A) 9 m/s
B) 3 m/s
C) 1 m/s
D) 0.33 m/s
E) 0.11 m/s

Question 68

A fluid of density 9.1 *10² kg/m³ is flowing through a tube at a speed of 5.3 m/s. What is the kinetic energy density of the fluid?

A) cannot be calculated without knowing the pressure
B) cannot be calculated without knowing the elevation
C) 4.8 *10³ J/m³
D) 1.3 *10⁴ J/m³
E) 2.5* 10⁶ J/m³

Question 69

A lawn sprinkler is made of a 1.0 cm diameter garden hose with one end closed and 25 holes, each with a diameter of 0.050 cm, cut near the closed end. If water flows at 2.0 m/s in the hose, the speed of the water leaving a hole is:

A) 2.0 m/s
B) 32 m/s
C) 40 m/s
D) 600 m/s
E) 800 m/s

Question 70

The quantity y appearing in Bernoulli's equation MUST be measured:

A) upward from the center of the Earth
B) upward from the surface of the Earth
C) upward from the lowest point in the flow
D) downward from the highest point in the flow
E) upward from any convenient level

Question 71

One end of a cylindrical pipe has a radius of 1.5 cm. Water (density = 1.0 *10³ kg/m³) streams steadily out at 7.0 m/s. The volume flow rate is:

A) 4.9 * 10^-3 m³/s
B) 2.5 m³/s
C) 4.9 m³/s
D) 7.0 m³/s
E) 48 m³/s

Question 72

A constriction in a pipe reduces its diameter from 4.0 cm to 2.0 cm. Where the pipe is narrow the water speed is 8.0 m/s. Where it is wide the water speed is:

A) 2.0 m/s
B) 4.0 m/s
C) 8.0 m/s
D) 16 m/s
E) 32 m/s

Question 73

Which of the following assumptions is NOT made in the derivation of Bernoulli's equation?

A) assume streamline flow
B) neglect viscosity
C) neglect friction
D) neglect gravity
E) neglect turbulence

Question 74

Which of the following is true?

A) A streamline can only be defined for irrotational flow.
B) A streamline cannot be defined for turbulent flow.
C) Streamlines cannot cross in laminar flow, but can cross in turbulent flow.
D) A streamline is the path that a tiny element of fluid would take as the fluid flows.
E) The velocity vector of a fluid element is always perpendicular to the streamline.

Question 75

A fluid is undergoing steady flow. Therefore:

A) the velocity of any given molecule of fluid does not change
B) the pressure does not vary from point to point
C) the velocity at any given point does not vary with time
D) the density does not vary from point to point
E) the flow is not uphill or downhill

Question 76

A large water tank, open at the top, has a small hole in the bottom. When the water level is 30 m above the bottom of the tank, the speed of the water leaking from the hole:

A) is 2.5 m/s
B) is 24 m/s
C) is 44 m/s
D) cannot be calculated unless the area of the hole is given
E) cannot be calculated unless the areas of the hole and tank are given

Question 77

One end of a cylindrical pipe has a radius of 1.5 cm. Water (density = 1.0* 10³ kg/m³) streams steadily out at 7.0 m/s. The rate at which mass is leaving the pipe is:

A) 2.5 kg/s
B) 4.9 kg/s
C) 7.0 kg/s
D) 48 kg/s
E) 7.0 * 10³ kg/s

Question 78

Water (density = 1.0 * 10³ kg/m³) flows through a horizontal tapered pipe. At the wide end its speed is 4.0 m/s. The difference in pressure between the two ends is 4.5 *10³ Pa. The speed of the water at the narrow end is:

A) 2.6 m/s
B) 3.2 m/s
C) 4.0 m/s
D) 4.5 m/s
E) 5.0 m/s

Question 79

Consider a pipe containing a fluid, with the fluid being at rest. To apply Bernoulli's equation to this situation:

A) set v equal to zero because there is no motion
B) set g equal to zero because there is no acceleration
C) set v and g both equal to zero
D) set p equal to the atmospheric pressure
E) cannot be done, Bernoulli's equation applies only to fluids in motion

Question 80

A large tank filled with water has two holes in the bottom, one with twice the radius of the other. In steady flow the speed of water leaving the larger hole is ________ the speed of the water leaving the smaller.

A) twice
B) four times
C) half
D) one-fourth
E) the same as