Deck 9: Solids and Fluids

Question 1

Distinguish between stress and strain.

Answer 1

Stress is a measure of the force causing a deformation. Strain is a relative measure of the deformation resulting from application of a stress.

Question 2

What is the maximum depth from which a pump on the surface can "suck" up water?

Answer 2

Atmospheric pressure will support a column of water about 10. m high.

Question 3

When a heavy barge floats above a fish swimming in the water below, does the PRESSURE exerted upon the fish change (and why)?

Answer 3

NO. The barge displaces just enough water to equal its weight. The barge can be replaced by water up to the water surface and the weight of that overlying material is the same upon the fish.

Question 4

An object is submerged in a swimming pool and of course the water exerts a buoyant force on the object. Suppose a thousand gallons of oil is spilled into the pool and now floats above the water. How is the buoyant force on the object changed by the overlying oil?

Question 5

An object will float in a fluid if the average density of the object is greater than the density of the fluid.

Question 6

An object completely submerged in water must either rise or fall.

Question 7

Steady flow means that all the particles of a fluid have the same velocity as they pass a given point.

Question 8

Irrotational flow means that a fluid element experiences a net angular velocity.

Question 9

Incompressible flow means that the fluid's density is constant.

Question 10

Stress is

A) the same as force.
B) the strain per unit length.
C) the ratio of the change in length.
D) applied force per cross-sectional area.

Question 11

Strain is

A) the stress per unit area.
B) the ratio of the change in length to the original length.
C) the ratio of stress to elastic modulus.
D) the applied force per unit area.

Question 12

Young's modulus is a(n)

A) strain.
B) elastic modulus.
C) stress.
D) breaking strength.
E) pressure limit.

Question 13

The slope of the straight line shown on the graph in Figure 9-1 is called the

A) compressibility.
B) Young's modulus.
C) bulk modulus.
D) pressure.

Question 14

As one stretches a metal rod, which condition is first reached?

A) elastic limit
B) breaking point
C) fracture point
D) proportional limit

Question 15

A piece of iron sinks to the bottom of a lake where the pressure is 21. atm. Which statement best describes what happens to the volume of that piece of iron?

A) There has been no change in the volume of the iron.
B) Its volume decreases slightly.
C) Its volume increases slightly.
D) Its volume becomes 21. times greater.

Question 16

Which of the following is not a dimensionless number?

A) specific gravity
B) stress
C) strain
D) Reynolds number

Question 17

All of the following are dimensionless except

A) strain.
B) Reynolds number.
C) specific gravity.
D) bulk modulus.

Question 18

The weight that will cause a wire of diameter d to stretch a given distance, for a fixed length of wire, is

A) proportional to d.
B) independent of what the length of the wire is.
C) independent of d.
D) proportional to d².

Question 19

A piece of iron sinks to the bottom of a lake where the pressure is 21 atm. Which statement best describes what happens to the density of that piece of iron?

A) There has been no change in the density of the iron.
B) Its density increases slightly.
C) Its density decreases slightly.
D) Its density becomes 21 times greater.

Question 20

Which of the following is NOT a unit of pressure?

A) Pascal
B) psi
C) atmosphere
D) N.m²
E) inches of mercury

Question 21

The density of water is

A) 1.0 × 10³ kg/cm³.
B) 1.0 kg/m³.
C) 1.0 × 10^-3 g/m³.
D) 1.0 Mg/m³.
E) 1.0 × 10¹ kg/cm³.

Question 22

When you are scuba diving, the pressure on your face plate

A) is independent of both depth and orientation.
B) will be greatest when you are facing upward.
C) depends only on your depth, and not on how you are oriented.
D) will be greatest when you are facing downward.

Question 23

"Pressure applied to an enclosed fluid is transmitted to every point in the fluid and to the enclosure walls" is known as

A) Bernoulli's principle.
B) Pascal's principle.
C) Kepler's law.
D) Archimedes' principle.
E) Fermet's principle.

Question 24

A mercury barometer

A) is an open tube manometer.
B) is a closed tube manometer.
C) is usually 760. cm tall.
D) does not contain mercury.
E) measures gauge pressure.

Question 25

Atmospheric pressure does NOT correspond to approximately

A) 1.0 × 10² N/m².
B) 0.1 MPa.
C) 2.4 × 10² oz/in².
D) 2.2 × 10³ lb/ft².
E) 15. lb/in².

Question 26

Consider an object floating on a pool of water. Suppose much oil is poured onto the water and now floats above the water, with the object floating with part surrounded by a layer of oil and the lower part still in water. How has the buoyant force on the object changed by the oil layer?

A) increased
B) decreased
C) remained the same

Question 27

As a helium-filled dirigible rises in the atmosphere, the buoyancy force is expected to

A) increase.
B) decrease.
C) remain constant.

Question 28

A spherical inflated balloon is submerged in a pool of water. If it is further inflated so that its radius doubles, how is the buoyant force affected?

A) 8 times larger
B) not at all
C) 4 times larger
D) 2 times larger
E) 6 times larger

Question 29

A submarine rests on the sea bottom. The normal force exerted upon the sub by the sea-floor is equal to

A) the weight of the sub plus the weight of the displaced water.
B) the weight of the sub.
C) the weight of the sub less the weight of the displaced water.
D) the weight of the displaced water.
E) the buoyant force less 1 atmosphere acting on the sub.

Question 30

The pressure differential across a wing cross section due to the difference in air flow is explained by

A) Newton's third law.
B) Kepler's law.
C) Bernoulli's equation.
D) Archimedes Principle.
E) Poiseuille's law.

Question 31

Air is forced to flow over an object whose cross-section is shown in Figure 9-2.

The speed of the air flowing close to the top surface is ________ the speed of the air flowing close to the bottom surface.

A) less than
B) greater than
C) equal to

Question 32

Which has the greatest effect on the flow of fluid through a pipe? That is, if you made a 10% change in each of the quantities below, which would cause the greatest change in the flow rate?

A) the fluid viscosity
B) the length of the pipe
C) the fluid density
D) the radius of the pipe
E) the pressure difference

Question 33

A viscous oil flows through a narrow pipe. If the diameter of the pipe were doubled, the flow rate should increase by what factor?

A) 6
B) 4
C) 2
D) 8
E) 16

Question 34

COHESIVE FORCES are

A) attractive forces between unlike molecules.
B) attractive forces between like molecules.
C) repulsive forces between unlike molecules.
D) repulsive forces between like molecules.

Question 35

The SAE grade (e.g. SAE 20W) is an indicator of oil

A) pressure.
B) surface tension.
C) viscosity.
D) density.
E) Reynolds number.

Question 36

When a baseball pitcher throws a curve ball, he makes the ball spin about an axis ________ the direction in which the ball's center of mass is moving.

A) perpendicular to
B) parallel to
C) 45° with respect to

Question 37

If a liquid does not wet the inner surface of a capillary tube inserted into it, the cohesion of the liquid is ________ the adhesion between the liquid and surface.

A) greater than
B) less than
C) the same as

Question 38

When soup gets cold, it often tastes greasy. This "greasy" taste seems to be associated with oil spreading out all over the surface of the soup, instead of staying in little globules. This is readily explained in terms of

A) the decrease in the surface tension of water with increasing temperature.
B) the Bernoulli effect.
C) the increase in the surface tension of water with increasing temperature.
D) Archimedes Principle.
E) Poiseuille's law.

Question 39

When a small spherical rock of radius r falls through water, it experiences a drag force (a) is its velocity and "a" is a constant proportional to the viscosity of water. From this, one can deduce that if a rock of diameter 2 mm falls with terminal velocity, "v," then a rock of diameter 4 mm will fall with terminal velocity

A) 2 v.
B) 4 v.
C) v / 4.
D) v.
E) v / 2.

Question 40

Two Styrofoam balls, of radii R and 2R, are released simultaneously from a tall tower. Which will reach the ground first?

A) the larger one
B) Both will reach the ground simultaneously.
C) the smaller one
D) The result will depend on the atmospheric pressure.

Question 41

When a tube of diameter d is placed in water, the water rises to a height h. If the diameter were half as great, how high would the water rise?

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

Question 42

A narrow tube is placed vertically in a pan of water, and the water rises in the tube to 4 cm above the level of the pan. The surface tension in the liquid is lowered to one-half its original value by the addition of some soap. What happens to the height of the liquid column in the tube?

A) It drops or rises, but the height cannot be calculated from the information given.
B) It remains at the same height.
C) It drops to 2 cm.
D) It drops to 1 cm.

Question 43

A mass of 50. kg is suspended from a steel wire of diameter 1.0 mm and length 11.2 m. How much will the wire stretch? (The Young's modulus for steel is 20 × 10¹⁰ N/m².)

Question 44

At a depth of about 1030. m in the sea the pressure has increased by 100. atmospheres (to about 10⁷ N/m²). By how much has 1 m³ of water been compressed by this pressure? The bulk modulus of water is 2.3 × 10⁹ N/m².

Question 45

A wire of diameter 1.0 mm and length 3.5 m stretches 3.5 mm when 8.0 kg is hung from it.
(a) What is the Young's modulus for the wire?
(b) What is the effective spring constant for the stretching wire?

Question 46

7.0 kg is hung from a steel wire of diameter 0.75 mm and length 2.5 meters.
(S = 8.2 × 10¹⁰ N/m²; Y = 20 × 10¹⁰ N/m²)
(a) By how much does the wire stretch?
(b) If the wire diameter were doubled, what would be the stretch?

Question 47

A window for viewing fish in the local aquarium is square and measures
0.8 m × 0.8 m. Its center is 12. m below the surface. What is the total force on the window?

Question 48

Suppose that in an examination of a spinal injury it is found that the spinal fluid (with about the same density as water) will rise a vertical height of 13. cm in an open tube. What pressure does this correspond to, expressed in mm of mercury and in atmospheres?

Question 49

What is the gauge pressure at a depth of 100 m. in water?

Question 50

Consider diving 20.0 m below the surface of the ocean (density 1.03 grams/cc)
(a) what is the gauge pressure at that depth, in atmospheres?
(b) what is the absolute pressure at that depth, in atmospheres?
(c) If you were in a submarine at that depth, what would be the total force on a 100. cm2 window?

Question 51

Consider a submarine at a depth of 67. meters in sea water (density 1.03 grams/cc) and the interior of the sub is at 1.0 atmosphere.
(a) What is the outside pressure at that depth?
(b) Find the total force that must be withstood by a square hatch (0.90 m square) which leads to the sub interior.

Question 52

A spherical hot air balloon of diameter 20. meters just floats (hovers) when the hot air inside has been heated to a density of 1.00 kg/m³. What is the weight of the balloon and cargo (not including the air inside) if the surrounding air has a density of 1.30 kg/m³?

Question 53

An iron barge 25. m long and 4.0 m wide has a mass of 100,000.kg. What minimum depth of water is needed to float it?

Question 54

Oil of specific gravity 0.90 is poured on top of a beaker of water. A cube of plastic of specific gravity 0.95 is placed in the liquid. What fraction of the cube will be immersed in water?

Question 55

A polar bear of mass 200. kg stands on an ice floe 100. cm thick. What is the minimum area of the floe that will just support the bear in saltwater of specific gravity 1.03? The specific gravity of ice is 0.98.

Question 56

A cylindrical rod of length 12. cm and diameter 2.0 cm will just barely float in water. What is its mass?

Question 57

A sphere of diameter 7.9 cm is completely submerged in water and seems to weigh 32.0% less in the water than out of it.
(a) What is the density of the sphere?
(b) If the sphere had been twice as dense, it would have weighed what % less in water than out?

Question 58

A long telephone pole (wood density 0.80 kg/m³) is vertically lowered into a slightly larger vertical pipe which is filled with salt water of density 1.04 kg/m³. The pole ends up floating with what percent of the pole above the water?

Question 59

A crane lifts a steel submarine (density = 7.8 × 10³ kg/m³) of mass 20,000 kg. What is the tension in the lifting cable:
(a) when the submarine is submerged?
(b) when it is entirely out of the water?

Question 60

An incompressible fluid flows at 0.252 m/s through a 44. mm diameter (circular cross section) (a) section?
(b) what is the flow rate in liters/minute?

Question 61

A hole of radius 1.0 mm occurs in the bottom of a water storage tank that holds water at a depth of 15 m. At what rate will water flow out of the hole?

Question 62

An ideal fluid in a pipe of diameter 14. cm is moving at 6.0 m/s.
(a) If the incompressible fluid density is 1.05 grams/cc, what is the flow rate in kg/s?
(b) What is the speed of flow if the pipe narrows to 4.0 cm radius?

Question 63

By how much will mercury rise (or fall) in a 1.0 mm diameter glass tube (contact angle 140.°, Hg density 13.6 g/cc, surface tension 0.45 N/m)?

Question 64

The surface tension of water is 0.073 N/m. How high will water rise in a capillary tube of diameter 1.20 mm?

Question 65

Suppose that the build-up of fatty tissue on the wall of an artery decreased the radius by 10%. By how much would the pressure provided by the heart have to be increased to maintain a constant blood flow?

Question 66

A copper wire is found to break when subjected to minimum tension of 36. N. If the wire diameter were half as great, we would expect the wire to break when subjected to a minimum tension of

A) 18 N
B) 26. N
C) 51. N
D) 9.0 N
E) 36. N

Question 67

Suppose that an 80. kg person walking on crutches supports all his weight on the two crutch tips, each of which is circular with a diameter of 1.0 inch. What pressure is exerted on the floor? Express the answer in psi.

A) 14. psi
B) 1.4 × 10² psi
C) 1.1 × 10² psi
D) 56 psi
E) 2.2 × 10² psi

Question 68

A plastic block of dimensions 2.0 cm × 3.0 cm × 4.0 cm has a mass of 30. grams. What is its density?

A) 0.80 g/cm³
B) 1.2 g/cm³
C) 1.6 g/cm³
D) 1.3 g/cm³
E) 2.3 g/cm³

Question 69

A circular window of 30.0 cm diameter in a submarine can withstand a maximum force of 1.88 × 10⁶ N. What is the maximum depth to which the submarine can go without damaging the window?

A) 1.20 km
B) 945 m
C) 1.33 km
D) 2.70 km
E) 750 m

Question 70

Instead of cables, a hydraulic lift raises an elevator weighing 2.5 kiloNewtons. The input piston has a 2.0 cm diameter and the lift piston has a 28. cm diameter (See Figure 9-3)

What minimum force must be applied to the input piston?

A) 0.49 MN
B) 35. kN
C) 2.5 kN
D) 13. N
E) 0.18 kN

Question 71

A ship that weighs 10,000 tons (mass 10 million kg) must displace what volume of fresh water in order to float?

A) 10¹⁰m³
B) 10¹²m³
C) 10⁴m³
D) 10⁷m³
E) 10⁸m³

Question 72

A container of water is placed on a scale, and the scale reads 120. g. Now a 20.0g piece of copper (specific gravity = 8.90) is suspended from a thread and lowered into the water, not touching the bottom of the container. What will the scale now read?

A) 140 g
B) 122 g
C) 138 g
D) 112 g
E) 120 g

Question 73

A sunken steel ship has a mass of 500,000 kg. It is filled with water. In order to lift the ship, air bags are to be inflated inside the hull. What volume of air is needed if 7.8 is the specific gravity of steel?

A) 436 m³
B) 872 m³
C) 2778 m³
D) 225 m³
E) 1266 m³

Question 74

Water flows through a horizontal pipe of cross-sectional area 10. cm² at a pressure of 0.25 atm. The flow rate is 1.0 L/s. At a valve, the effective cross-sectional area of the pipe is reduced to 5.0 cm². What is the pressure at the valve?

A) 0.112 atm
B) 0.235 atm
C) 0.200 atm
D) 7.7 × 10³ Pa
E) 0.157 atm

Question 75

SAE No. 10 oil has a viscosity of 0.20 Pa-s. How long would it take to pour 4.0 L of oil through a funnel with a neck 15. cm long and 2.0 cm in diameter? (Assume the surface of the oil is kept 6.0 cm above the top of the neck, and neglect any drag effects due to the upper part of the funnel.)

A) 52 s
B) 84 s
C) 105 s
D) 1.5 minutes
E) 46 s