Deck 13: Fluids

Question 1

A football coach in hopes of improving his kicker's performance fills a 0.9 kg football with helium rather than air.Assuming that the football contains a volume of helium equal to the air it replaces at standard temperature and pressure,what change in relative weight of the football (change in weight divided by weight)is to be expected? The volume of the football is 1.6 l.

A)1.81 × 10^-3
B)1.42 × 10^-3
C)1.96 × 10^-4
D)1.01 × 10^-3

Answer 1

1.81 × 10^-3

Question 2

A compressed gas with a total mass of 203 kg is stored in a spherical container that has a radius of 0.521 m.What is the density of the compressed gas?

A)343 kg/m³
B)209 kg/m³
C)254 kg/m³
D)305 kg/m³

Answer 2

343 kg/m³

Question 3

Calculate the pressure exerted on the ground by a 79 kgperson standing on one foot.Assume that the bottom of the person's foot is 13 cm wide and 28 cm long.

A)2.1 × 10⁴ Pa
B)2.2 × 10³ Pa
C)4.8 × 10⁴ Pa
D)5.3 × 10⁴ Pa

Answer 3

2.1 × 10⁴ Pa

Question 4

An aspirator operates as a pump.Water flows by a small tube perpendicular to the flow of the water.If the water flows at 3.7 m/s,what pressure differential is present if the other end of the tube is maintained at atmospheric pressure?

A)0.93 atm
B)0.69 atm
C)0.31 atm
D)-0.31 atm

Question 5

One of the dangers of tornados and hurricanes is the rapid drop in air pressure that is associated with such storms.Assume that the air pressure inside of a sealed house is 1.02 atm when a hurricane hits.The hurricane rapidly decreases the external air pressure to 0.910 atm.What net force (directed outwards)is exerted on a 2.02 m square window on the house?

A)4.55 × 10⁴ N
B)5.14 × 10⁴ N
C)4.78 × 10⁵ N
D)5.37 × 10⁵ N

Question 6

A container has a vertical tube,whose inner radius is 12.00 mm,connected to it at its side.An unknown liquid reaches level A in the container and level B in the tube-level A being 5.0 cm higher than level B.The liquid supports a 20.0 cm high column of oil,between levels B and C,whose density is 320 kg/m³.In the figure,the gauge pressure at level B is closest to:

A)630 Pa
B)310 Pa
C)470 Pa
D)790 Pa
E)940 Pa

Question 7

A water tank is filled to a depth of 10 m and the tank is 20 m above ground.The water pressure at ground level in a hose 2 cm in diameter is closest to:

A)3.9 × 105 N/m²
B)2.0 × 104 N/m²
C)9.2 N/m²
D)The cross-sectional area of the tank is needed.

Question 8

A pump uses a piston of 15 cm diameter which moves 2 cm/s.What is the fluid velocity of a tube 3 mm in diameter?

A)50 m/s
B)50 cm/s
C)6 cm/s
D)22 cm/s

Question 9

How many logs 3.00 m long and 18.0 cm in diameter are needed to just barely float a 2500.0 kg car? (ρwood = 0.720 g/cm³)

A)118
B)117
C)30
D)29

Question 10

A standard atmosphere has a pressure versus altitude relation approximated by

With α = 0.116 km-1.An aircraft flies at 30,000 ft but maintains a cabin pressure of that at
8000 ft.What force is exerted by air pressure on a square meter of cabin wall area?

A)4.1 × 10⁴ N
B)124 N
C)3.5 × 10⁴ N
D)7.6 × 10⁴ N

Question 11

A house is supported equally on 18 pilings each with a 0.5 m² area at the base.The soil can withstand 5 psi.What could be the maximum mass of the house?

A)3.2 × 10⁴ kg
B)6.3 × 10⁴ kg
C)8.0 × 10⁴ kg
D)1.6 × 10⁴ kg

Question 12

The body takes a mass of air into the lungs directly proportional to the ambient pressure.A diver who uses 27 psi/min at sea level has an air tank initially containing 1800 psi.How long can the diver work at a water depth of 40.0 ft.?

A)31 min
B)56 min
C)107 min
D)2 min

Question 13

A tank of water at rest is 2.0000 m deep.It is then accelerated at 5.0000 m/s² parallel to the original water surface,so that the front edge of the water in the tank is lowered to 1/2 its original value.What is the water pressure in the tank at the bottom back edge?

A)29,430.0013 N/m²
B)9 N/m²
C)9810.00042 N/m²
D)The length of the tank is needed.

Question 14

The density of material at the center of a neutron star is approximately 1.00 × 10¹⁸ kg/m³.Calculate the mass of a cube of this material that is 1.76 microns on each side.One micron is equal to 1 × 10^-6 m.

A)5.45 kg
B)4.74 kg
C)6.16 kg
D)6.70 kg

Question 15

A submarine in neutral buoyancy is 100 m below the surface of the water.What air pressure must be supplied to remove water from the ballast tanks in order for the submarine to surface?

A)9.9 × 105 N/m²
B)9.8 × 105 N/m²
C)4.9 × 105 N/m²
D)The cross-sectional area of the tank is needed.

Question 16

A container has a vertical tube,whose inner radius is 24.00 mm,connected to it at its side.An unknown liquid reaches level A in the container and level B in the tube-level A being 5.0 cm higher than level B.The liquid supports a 20.0 cm high column of oil,between levels B and C,whose density is 570 kg/m³.In the figure,the mass of the oil,in grams,is closest to:

A)210
B)410
C)620
D)820
E)1000

Question 17

A cap 7.000 cm in diameter plugs an opening in a spherical container 1.000 m in diameter at atmospheric pressure.The container is submerged to a depth of 10.00 ft in water.What force is needed to remove the plug? Assume the plug is planar and the pressure over the container is equalized.

A)115 N
B)460 N
C)4.608 × 10⁶ N
D)378 N

Question 18

Water is pumped out of a well at 5.000 m/s through a 8.000 cm diameter hose.The well is 30.00 ft deep.What power is needed by the pump?

A)2253 W
B)230 W
C)6894 W
D)The area of the well is needed.

Question 19

A hollow steel ball of diameter 3 m barely floats in water.What is the wall thickness of the ball? (ρFe = 7.87 g/cm³)

A)6.6 cm
B)37 cm
C)131 cm
D)79 cm

Question 20

A 4.7 kg solid sphere,made of metal whose density is 4000 kg/m3,is suspended by a cord.The density of water is 1000 kg/m³.When the sphere is immersed in water,the tension in the cord is closest to:

A)35 N
B)40 N
C)46 N
D)52 N
E)58 N

Question 21

If the gauge pressure at a certain depth in Lake Michigan is 3.5 atmospheres,the absolute pressure at that depth is 4.5 atm.

Question 22

An air bubble underwater has the same pressure as that of the water.As the air bubble rises toward the surface (and its temperature remains constant),the volume of the air bubble

A)increases.
B)decreases.
C)remains constant.
D)increases or decreases,depending on the rate it rises.

Question 23

How much would a lead brick 2.0 in × 2.0 in × 8.0 in weigh if placed in oil with density ρ = 0.92 g/cm³? (ρPb = 11.4 g/cm³)

A)5.5 kg
B)0.34 kg
C)6 kg
D)0.48 kg

Question 24

A rectangular wooden block measures 10.0 cm × 4.00 cm × 2.00 cm.When the block is placed in water,it floats horizontally,with its bottom face 1.65 cm below the surface.What is the density of the wood?

A)0.825 g/cm³
B)1.21 g/cm³
C)1.65 g/cm³
D)0.606 g/cm³
E)0.350 g/cm³

Question 25

A 9.8 kg solid sphere,made of metal whose density is 3000 kg/m³,is suspended by a cord.The sphere floats when placed in a liquid of density 4200 kg m3.The fraction of the volume of the sphere that is submerged is closest to:

A)0.71
B)0.73
C)0.75
D)0.69
E)0.67

Question 26

A venturi is constructed of a 9.0 cm diameter pipe with a 2.0 cm diameter throat.Water pressure in the pipe is twice atmospheric pressure and it flows with a velocity of 0.30 m/s. What is the pressure in the throat?

A)1.8 atm
B)0.18 atm
C)2.2 atm
D)2.0 atm

Question 27

A 200.0 kg flat-bottomed boat floats in fresh water,which has a density of 1000.0 kg/m³.Assuming that the base of the boat is 1.42 m wide and 4.53 m long,how much of the boat is submerged when it carries three passengers whose total mass is 193 kg?

A)6.11 cm
B)6.48 cm
C)6.84 cm
D)7.33 cm

Question 28

A long vertical metal cylinder is filled with oil.If a piston pushes on the top of this cylinder and increases the pressure there by 6,000 Pa,the pressure at the bottom will increase considerably more due to the weight of the oil.

Question 29

If a uniform sphere is compressed to half of its original diameter,its mass remains the same but its density becomes 8 times as great.

Question 30

A 8.6 kg solid sphere,made of metal whose density is 3400 kg/m³,is suspended by a cord.When the sphere is immersed in a liquid of unknown density,the tension in the cord is 38 N.The density of the liquid is closest to:

A)1900 kg/m³
B)1700 kg/m³
C)1600 kg/m³
D)1500 kg/m³
E)1400 kg/m³

Question 31

When an object is floating,the buoyant force on it is just equal to its weight.

Question 32

Water flows through a pipe having a varying width.More water flows per second through the wide section than through the narrow section because there is more room for it to flow.

Question 33

If the hydrostatic pressure at a certain depth in the ocean is 2 atm,the hydrostatic pressure will be 4 atm if you go twice as deep.

Question 34

A pressurized cylindrical tank,5.0 m in diameter,contains water that emerges from the pipe at point C,with a velocity of 13 m/s.Point A is 10 m above point B and point C is 3 m above point B.The area of the pipe at point B is 0.08 m² and the pipe narrows to an area of 0.04 m² at point C.Assume the water is an ideal fluid in laminar flow.The density of water is 1000 kg/m³.In the figure,the mass flow rate in the pipe is closest to:

A)520 Kg/s
B)470 Kg/s
C)420 Kg/s
D)360 Kg/s
E)310 Kg/s

Question 35

According to Pascal's principle,if you increase the pressure enough so that the force at one end of an oil-filled tube increases by 10 N,the force will increase at all points in the tube by 10 N.

Question 36

Consider a very small hole in the bottom of a tank 20.0 cm in diameter filled with water to a height of 50.0 cm.Find the speed at which the water exits the tank through the hole.

A)3.13 m/s
B)9.80 m/s
C)31.8 m/s
D)34.9 m/s

Question 37

The Tonga Trench in the Pacific Ocean is 36,000 feet deep.Assuming that sea water has an average density of 1.04 g/cm³,calculate the absolute pressure at the bottom of the trench in atmospheres.

A)1.1 × 10³ atm
B)1.1 × 10⁸ atm
C)1.1 × 10⁵ atm
D)1.1 × 10⁶ atm
E)2.1 atm

Question 38

How many grams of ethanol (specific gravity 0.80)should be added to 5 grams of chloroform (specific gravity 1.50)if the resulting mixture is to have a specific gravity of 1.20?

A)2.0 g
B)2.4 g
C)1.8 g
D)4.4 g
E)1.6 g

Question 39

If you increase the pressure on the surface of a can of water,you will increase the buoyant force on objects placed in that water.

Question 40

Water flowing through a pipe suddenly comes to a section of pipe where the pipe diameter decreases to 86% of its previous value.If the speed of the water in the larger section of the pipe was 32 m/s,what is its speed in this smaller section?

A)43 m/s
B)37 m/s
C)28 m/s
D)24 m/s

Question 41

A tire of an automobile has a gauge pressure of 30 psi at the top of a mountain,and the air temperature inside the tire is 300 K.The atmospheric pressure at the top of the mountain is 0.7 atm.The car is driven down to sea level,where the atmospheric pressure is 1.0 atm,and the air inside the tire is heated to 350 K.At sea level,assuming no leaks,the gauge pressure of the tire will be

A)lower.
B)higher.
C)the same.

Question 42

The tires of a car support the weight of a stationary car.If one tire has a slow leak,the air pressure within the tire will _______ with time,the surface area between the tire and the road will ________ with time,and the net force the tire exerts on the road will ___________ with time.

A)decrease,increase,remain constant
B)decrease,increase,decrease
C)decrease,decrease,decrease
D)increase,increase,increase
E)decrease,increase,increase

Question 43

A barge loaded with lumber and iron ore floats in a lock by a dam (a closed pool of water like a big swimming pool).If some of the cargo is thrown overboard,the level of water in the lock will

A)rise.
B)drop.
C)stay the same.
D)rise,provided it is lumber that is thrown overboard.
E)rise,provided it is iron ore that is thrown overboard.

Question 44

A spherical ball of lead (density 11.3 g/cm³)is placed in a tub of mercury (density 13.6 g/cm³).Which answer best describes the result?

A)The lead ball will float with about 83% of its volume above the surface of the mercury.
B)The lead ball will float with its top exactly even with the surface of the mercury.
C)The lead ball will float with about 17% of its volume above the surface of the mercury.
D)The lead will sink to the bottom of the mercury.
E)None of the above

Question 45

In England in the Middle Ages an extensive system of canals was used for transportation.Some of these canals crossed over canyons by flowing over bridges (viaducts).Suppose that a heavily loaded barge crossed over such a waterway bridge.

A)The force downward on the bridge would increase because of the added weight of the barge.
B)The force on the bridge would not change when the barge passed over.
C)The force on the barge would become less because some water would be squeezed off of the bridge.
D)The force on the bridge would become less because of the buoyancy effect of the water on the barge.
E)Whether or not the force on the bridge would increase or decrease would depend on whether the water was flowing or stationary.

Question 46

Consider a brick that is totally immersed in water.The long edge of the brick is vertical.The pressure on the brick is

A)the same on all surfaces of the brick.
B)greatest on the face with largest area.
C)greatest on the top of the brick.
D)greatest on the sides of the brick.
E)greatest on the bottom of the brick.

Question 47

The Bernoulli effect is described by the equation

The origin of this relation is that it is a statement of

A)the conservation of linear momentum.
B)Newton's Third Law,i.e. ,equal action and reaction.
C)the conservation of energy for a moving fluid.
D)the continuity principle for fluids.
E)F = ma as applied to a fluid.

Question 48

A wooden block contains some nails so that its density is exactly equal to that of water.If it is placed in a tank of water and released from rest when it is completely submerged,it will

A)rise to the surface.
B)sink to the bottom.
C)remain where it is released.

Question 49

The Bernoulli effect is responsible for the lift force on an airplane wing.Wings must therefore be designed so as to insure that

A)air molecules will be deflected downward when they hit the wing.
B)air molecules will be deflected upward when they hit the wing.
C)air molecules move more rapidly past the upper surface of the wing than past the lower surface.
D)air molecules move more rapidly past the lower surface of the wing than past the upper surface.
E)wings are thick enough to create a significant pressure difference between the top and bottom surfaces of the wings because of the different heights of these surfaces.

Question 50

In the figure,fluid fills the container shown here.At which of the indicated points is the pressure greatest?

A)A
B)B
C)C
D)D
E)The pressure is the same at each of the labeled points.

Question 51

A waitress fills your water glass with ice water (containing many ice cubes)such that the liquid water is perfectly level with the rim of the glass.As the ice melts,

A)the liquid-water level remains flush with the rim of the glass.
B)the liquid-water level rises,causing water to run down the outside of the glass.
C)the liquid-water level decreases.