Deck 5: Fluid Mechanics

Question 1

Water pressure is greatest against the

A)top of a submerged object.
B)bottom of a submerged object.
C)sides of a submerged object.
D)same against all surfaces.
E)none of the above

Answer 1

B

Question 2

As a woman holding her breath swims deeper and deeper in a lake, her density

A)increases.
B)decreases.
C)remains the same.

Answer 2

A

Question 3

Blood pressure is normally greater in your

A)ears.
B)feet.
C)same in each.

Answer 3

B

Question 4

If a loaf of bread is compressed, its

A)molecules decrease in size.
B)density decreases.
C)density increases.
D)none of the above

Question 5

The pressure in a liquid depends on liquid

A)density.
B)depth.
C)both
D)neither

Question 6

When you stand on tiptoes on a bathroom scale, there is an increase in

A)weight reading.
B)pressure on the scale, not registered as weight.
C)both weight and pressure on the scale.
D)none of the above

Question 7

The density of air at room temperature is about 1.2 grams/cm³. Estimate the mass of air inside an average automobile.

A)2 grams
B)2 kg
C)20 kg
D)200 kg
E)2000 kg

Question 8

When a chocolate bar is cut in half, its density is

A)halved.
B)unchanged.
C)doubled.

Question 9

There is a legend of a Dutch boy who bravely held back the Atlantic Ocean by plugging a leak near the top of a dike with his finger until help arrived. Which of the following is most likely?

A)the huge size of the Atlantic Ocean makes this impossible
B)force on his finger would be huge but pressure small enough
C)the force on his finger would have been less than 1 N
D)both the force and pressure on his finger would have been huge, but not too huge for a public-spirited Dutch lad
E)none of the above

Question 10

Which has the greater density, a lake full of water or a cupful of lake water?

A)the cupful of lake water
B)the lake
C)both have the same density

Question 11

Compared to a bar of pure gold, the density of a pure gold ring is

A)less.
B)the same.
C)more.

Question 12

Water pressure at the bottom of a lake depends on the

A)weight of water in the lake.
B)surface area of the lake.
C)depth of the lake.
D)all of the above

Question 13

The pressure at the bottom of a jug filled with water does NOT depend on

A)the acceleration due to gravity.
B)water density.
C)the height of the liquid.
D)surface area of the water.
E)none of the above

Question 14

Consider two tubes filled with water at the same height, one with fresh water and the other tube with salt water. The pressure is greater at the bottom of the tube with

A)fresh water.
B)salt water.
C)both the same
D)depends on whether the tubes have the same cross-sectional area.

Question 15

The density of air at room temperature is about 1.2 grams/cm³. This is the same as

A)12 kg/m³.
B)120 kg/m³.
C)1200 kg/m³.

Question 16

Compared to the density of a kilogram of feathers, the density of a kilogram of lead is

A)less.
B)more.
C)the same.

Question 17

As a swimmer dives deeper and deeper, strictly speaking, the volume of water displaced by the swimmer actually

A)decreases.
B)increases.
C)remains unchanged but pressure on her increases.
D)none of the above

Question 18

If the mass of an object were to double with no change in volume, its density would

A)be half.
B)double.
C)unchanged.

Question 19

If the volume of an object were to double with no change in mass, its density would

A)be half.
B)double.
C)unchanged.

Question 20

A dam is thicker at the bottom than at the top because

A)water is denser at deeper levels.
B)water pressure is greater at deeper levels.
C)water is cooler at deeper levels.
D)dams look better.
E)none of the above

Question 21

Fill a U-tube with water and the level in both ends is the same. Water seeks its own level. Why?

Question 22

What is the weight of water displaced by a 100-ton floating ship?

A)less than 100 tons
B)100 tons
C)more than 100 tons
D)100 cubic meters
E)depends on the ship's shape

Question 23

A lobster crawls onto a bathroom scale submerged on the ocean bottom. Compared to its weight above the surface, its apparent weight under water is

A)greater.
B)less.
C)the same.

Question 24

Compared to the density of water, the density of a fish is

A)more.
B)less.
C)the same.

Question 25

When an object is partly or wholly immersed in a liquid, it is buoyed up

A)by a force equal to its own weight.
B)by a force equal to the weight of liquid displaced.
C)and floats because of Archimedes' principle.
D)but sinks.
E)none of the above

Question 26

Buoyant force acts upward on a submerged object because

A)it acts in a direction to oppose gravity.
B)if it acted downward, nothing would float.
C)the weight of fluid displaced reacts with an upward force.
D)pressure up on bottom is greater than downward pressure on top of the object.

Question 27

What is the buoyant force acting on a 10-ton ship floating in a fresh-water lake?

A)less than 10 tons
B)10 tons
C)more than 10 tons
D)not enough information

Question 28

The density of a submarine cruising beneath the ocean surface has the same density as

A)a crab.
B)iron.
C)a floating submarine.
D)water.
E)none of the above

Question 29

What is the buoyant force acting on a 10-ton ship floating in the ocean?

A)less than 10 tons
B)10 tons
C)more than 10 tons
D)depends on density of seawater

Question 30

Clearly distinguish between pressure and force in the case of weighing yourself on a common bathroom scale.

Question 31

One liter of water has a mass of

A)1 kg.
B)1 N.
C)both
D)neither

Question 32

A completely submerged object always displaces its own

A)volume of fluid.
B)weight of fluid.
C)density of fluid.
D)all of the above
E)none of the above

Question 33

The reason a life jacket helps you float is that

A)the jacket causes you to weigh less.
B)the jacket has the same density as an average human.
C)the jacket repels water.
D)if you sink, the jacket sinks.
E)the combined density of you and the jacket is less than your density alone.

Question 34

Wood from the Lignum vitae tree in South America is denser than water. Could a boat be made with this wood? A raft? Briefly explain.

Question 35

The buoyant force on an object is less when the object is

A)partly submerged.
B)submerged near the surface.
C)submerged near the bottom.
D)none of the above

Question 36

What is the approximate density of a fish, compared with the density of water? Defend your answer.

Question 37

Two life preservers have identical volumes, one filled with Styrofoam and the other filled with sand. When both life preservers are fully submerged, the buoyant force is greater on the one filled with

A)Styrofoam.
B)sand.
C)same on each if volumes remain the same.

Question 38

Lobsters live on the bottom of the ocean. Compared with the density of seawater, the density of a lobster is

A)greater.
B)the same.
C)less.

Question 39

Pumice is a volcanic rock that floats. Compared with the density of water, its density is

A)less.
B)the same.
C)more.

Question 40

A fish normally displaces its own

A)volume of water.
B)weight of water.
C)both
D)neither

Question 41

An egg is placed at the bottom of a bowl filled with water. Salt is slowly added to the water until the egg rises and floats. From this experiment, we conclude that

A)egg-shell calcium is repelled by sodium chloride.
B)the density of salt water exceeds the density of the egg.
C)buoyant force does not always acts upward.
D)salt sinks to the bottom.
E)none of the above

Question 42

A boat loaded with a barrel of water floats in a swimming pool. When the barrel of water is poured overboard, the pool level

A)rises.
B)falls.
C)remains unchanged.

Question 43

If one caisson of the Falkirk Wheel carries a boat loaded with Styrofoam and the other carries a floating boat loaded with iron, the wheel would be

A)balanced.
B)out of balance.
C)unbalanced but still useful.
D)useless for lifting boats.

Question 44

A boat loaded with scrap iron floats in a swimming pool. When the iron is thrown overboard, the pool level will

A)rise.
B)fall.
C)remain unchanged.

Question 45

Two equal-sized buckets are filled to the top with water. One of the buckets has a piece of wood floating in it, making its total weight

A)less than the weight of the other bucket.
B)equal to the weight of the other bucket.
C)more than the weight of the other bucket.

Question 46

The volume of water displaced by a floating 20-ton boat is

A)20 cubic meters.
B)the volume of 20 tons of water.
C)the volume of the boat.
D)depends on the shape of the ship's hull.
E)none of the above

Question 47

A rock suspended by a weighing scale weighs 3 N when submerged in water and 5 N out of water. What is the buoyant force on the rock?

A)8 N
B)5 N
C)3 N
D)2 N
E)none of the above

Question 48

When a 5-N block of wood floats in mercury the buoyant force on it is

A)less than 5 N.
B)5 N.
C)more than 5 N.

Question 49

The pair of water-filled caissons of the Falkirk Wheel have equal weights when

A)they carry equal-weight floating boats.
B)one carries a heavy floating boat and the other only water.
C)they carry unequal weights of floating boats.
D)all of the above
E)none of the above

Question 50

Two life preservers have identical volumes, one filled with Styrofoam and the other filled with sand. When each is worn by swimmers, one swimmer floats and the other sinks. Interestingly, the buoyant force is actually greater on the life preserver that

A)sinks.
B)floats.
C)same either way
D)none of the above

Question 51

Buoyant force is greatest on a submerged

A)10-N block of lead.
B)10-N block of aluminum.
C)same on each

Question 52

A block of Styrofoam floats on water while a same size block of lead lies submerged in the water. The buoyant force is greatest on the

A)lead.
B)Styrofoam.
C)same for both

Question 53

Buoyant force is greatest on a submerged 1 cubic centimeter block of

A)lead.
B)aluminum.
C)same on each

Question 54

Ice cubes submerged at the bottom of a liquid mixture indicate that the mixture

A)fails to produce a buoyant force on the ice.
B)has dissolved air in a liquid state.
C)is composed of open-structured crystals.
D)is less dense than ice.

Question 55

Compared with an empty ship, the same ship loaded with Styrofoam will float

A)higher in the water.
B)lower in the water.
C)at the same level in the water.

Question 56

If one of the caissons of the Falkirk Wheel contained a sunken boat, resting on its bottom, and the other carried a floating boat, the wheel balance would

A)still be maintained.
B)be upset and more energy would be needed for operation.
C)render the machine useless.
D)violate Archimedes' principle.

Question 57

Buoyant force is greatest on a submerged

A)1-kg block of lead.
B)1-kg block of aluminum.
C)same on each

Question 58

A liter-sized block of ordinary wood floats in water. The volume of water displaced is

A)less than 1 L.
B)1 L.
C)more than 1 L.
D)none of the above

Question 59

An iron ball is placed in a pie pan that floats in a bucket. The water level is marked at the side of the bucket. Then the iron ball is removed and allowed to sink in the bucket. The water line at the side of the bucket is

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

Question 60

When a boat sails from fresh water to salt water, the boat will float

A)lower in the water.
B)higher in the water.
C)at the same water level.

Question 61

If the part of an iceberg that extends above the water were suddenly removed, the

A)iceberg would sink.
B)buoyant force on the iceberg would soon decrease.
C)density of the iceberg would change.
D)pressure on the bottom of the iceberg would increase.
E)none of the above

Question 62

When an ice cube in a glass of water melts, the water level

A)rises.
B)falls.
C)remains the same.

Question 63

Three large ice cubes float in bathtubs, each filled to the brim with water. Cube A has large air bubbles in it. Cube B has unfrozen water in it. Cube C has an iron railroad spike in it. When the ice cubes melt

A)water level in C decreases while water levels in the other two tubs remain the same.
B)only the water in C will spill over.
C)water level in A remains unchanged while the other tubs spill over.
D)all tubs spill over.
E)all levels remain the same.

Question 64

Strictly speaking, gas pressure inside an inflated stretched balloon is

A)less than air pressure outside the balloon.
B)equal to air pressure outside the balloon.
C)slightly greater than air pressure outside the balloon.

Question 65

The product of gas pressure and volume for a given mass of gas is constant

A)if the temperature doesn't change.
B)whether or not temperature changes.
C)never.
D)none of the above

Question 66

When gas in a container is squeezed to half its volume at constant temperature, the gas pressure

A)is half.
B)doubles.
C)quadruples.
D)remains the same.

Question 67

When gas in a container is squeezed to half its volume, its density

A)halves.
B)doubles.
C)quadruples.
D)remains the same.

Question 68

When gas in a container expands to twice its volume, its density

A)is half.
B)doubles.
C)quadruples.
D)remains the same.

Question 69

We know that any body more dense than water will sink in water. Why?

Question 70

Explain in terms of buoyant force how a fish is able to rise and sink in water. Contrast this to the way a submarine rises and sinks.

Question 71

Explain why ships of any weight are balanced on the Falkirk Wheel.

Question 72

An ice cube that contains small pieces of iron floats on water. When the ice melts, the water level

A)rises.
B)falls.
C)remains unchanged.

Question 73

If a weighted air-filled balloon sinks in deep water, it will

A)likely sink to an equilibrium level before reaching the bottom.
B)likely burst if water pressure is great enough.
C)become less dense as it sinks.
D)be acted on by a continually decreasing buoyant force.
E)none of the above

Question 74

In a vacuum, a marshmallow becomes

A)larger.
B)smaller.
C)does not change.

Question 75

A wooden block with a piece of iron tied to its top floats in a bucket of water. If the wood and iron flips over so the iron is on the bottom, the water level at the side of the bucket

A)rises.
B)falls.
C)remains the same.

Question 76

If a battleship sinks in a canal lock, the water level in the lock

A)rises.
B)falls.
C)remains unchanged.

Question 77

An ice cube floating in a glass of water contains many air bubbles. When the ice melts, the water level

A)rises.
B)falls.
C)remains unchanged.

Question 78

A boat loaded with wood floats in a swimming pool. When the wood is thrown overboard, the pool level

A)rises.
B)falls.
C)remains unchanged.

Question 79

Compared to the buoyant force on you when floating in fresh water, buoyant force on you when floating in the dense water of the Dead Sea is

A)less because volume displacement is less.
B)more because of the greater density of fluid displaced.
C)the same.

Question 80

When gas in a container expands to twice its volume at constant temperature, the gas pressure

A)is half.
B)doubles.
C)quadruples.
D)remains the same.