Properties of Fluids Questions & Answers :: Fluid Mechanics

1. Which one is in a state of failure?

a) Solid
b) Liquid
c) Gas
d) Fluid

Answer: d

Explanation: A fluid is a Tresca material with zero cohesion. In simple words, fluid is in a state of failure.

2. A small shear force is applied on an element and then removed. If the element regains it’s original position, what kind of an element can it be?

a) Solid
b) Liquid
c) Fluid
d) Gaseous

Answer: a

Explanation: Fluids (liquids and gases) cannot resist even a small shear force and gets permanently deformed. Hence, the element must be a solid element.

3. In which type of matter, one won’t find a free surface?

a) Solid
b) Liquid
c) Gas
d) Fluid

Answer: c

Explanation: Solid molecules have a definite shape due to large intermolecular forces. In liquids, molecules are free to move inside the whole mass but rarely escape from themselves. Thus, liquids can form free surfaces under the effect of gravity. But, in case of gases, molecules tend to escape due to low forces of attraction. Thus, gases won’t form any free surface.

4. If a person studies about a fluid which is at rest, what will you call his domain of study?

a) Fluid Mechanics
b) Fluid Statics
c) Fluid Kinematics
d) Fluid Dynamics

Answer: b

Explanation: Fluid Mechanics deals with the study of fluid at rest or in motion with or without the consideration of forces, Fluid Statics is the study of fluid at rest, Fluid Kinematics is the study of fluid in motion without consideration of forces and Fluid Dynamics is the study of fluid in motion considering the application forces.

5. The value of the compressibility of an ideal fluid is

a) zero
b) unity
c) infinity
d) more than that of a real fluid

Answer: a

Explanation: Ideal fluids are incompressible which means they will have zero compressibility.

6. The value of the Bulk Modulus of an ideal fluid is

a) zero
b) unity
c) infinity
d) less than that of a real fluid

Answer: c

Explanation: Bulk modulus k is the reciprocal of compressibility fi.
k = 1fi
Ideal fluids are incompressible which means fi = 0. Thus, k will be infinity.

7. The value of the viscosity of an ideal fluid is

a) zero
b) unity
c) infinity
d) more than that of a real fluid

Answer: a

Explanation: Ideal fluids are non-viscous which means they will have zero viscosity.

8. The value of the surface tension of an ideal fluid is

a) zero
b) unity
c) infinity
d) more than that of a real fluid

Answer: a

Explanation: Ideal fluids haze zero surface tension but real fluids have some finite value of surface tension.

9. Which one of the following is the unit of mass density?

a) kg = m3
b) kg = m2
c) kg = m
d) kg = ms

Answer: a

Explanation: Mass Density(p) is defined as the mass(m) per unit volume(V ), i.e., p = m ⁄v
Thus, the unit of p is kg = m3.

10. The specific gravity of a liquid has

a) the same unit as that of mass density
b) the same unit as that of weight density
c) the same unit as that of specific volume
d) no unit

Answer: d

Explanation: The specific gravity of a liquid is the ratio of two similar quantities (densities) which makes it unitless.

11. The specific volume of a liquid is the reciprocal of

a) weight density
b) mass density
c) specific weight
d) specific volume

Answer: b

Explanation: Specific volume(v) is defined as the volume(V ) per unit mass(m).
v = v⁄m = 1 / m⁄v = 1⁄p
where p is the mass density.

12. Which one of the following is the unit of specific weight?

a) N = m3
b) N = m2
c) N = m
d) N = ms

Answer: a

Explanation: Specific weight(γ) is defined as the weight(w) per unit volume(V ), i.e.,
γ = w / v
Thus, unit of is N = m3.

13. Which one of the following is the dimension of mass density?

a) [M1L-3T0].
b) [M1 L3 T0].
c) [M0 L-3 T0].
d) [M0 L3 T0].

Answer: a

Explanation: Mass Density(p) is defined as the mass(m) per unit volume(V ), i.e.,
[p] = [m]/[v] = [m] /[L3] = [ML-3].

14. Which one of the following is the dimension of specific gravity of a liquid?

a) [M1L-3T0].
b) [M1 L0 T0].
c) [M0 L-3 T0].
d) [M0 L0 T0].

Answer: d

Explanation: The specific gravity of a liquid is the ratio of two similar quantities (densities) which makes it dimensionless.

15. Which one of the following is the dimension of specific volume of a liquid?

a) [M1L-3T0].
b) [M-1 L3 T0].
c) [M-1 L-3 T0].
d) [M0 L3 T0].

Answer: b

Explanation: Specific volume(v) is defined as the volume(V ) per unit mass(m). Thus,

[v] = [V]/[m] = [L3]/[M] = [M-1L3].

16. Which one of the following is the dimension of specific weight of a liquid?

a) [ML-3-2].
b) [ML3T-2].
c) [ML-2 T-2].
d) [ML2 T-2].

Answer: c

Explanation: Specific weight(γ) is defined as the weight(w) per unit volume(V ), i.e.,

17. Two fluids 1 and 2 have mass densities of p1 and p2 respectively. If p1 > p2, which one of the following expressions will represent the relation between their specific volumes v1 and v2?

a) v1 > v2
b) v1 < v2
c) v1 = v2
d) Cannot be determined due to insufficient information.

Answer: b

Explanation: Specific volume(v) is defined as the volume(V ) per unit mass(m).
v = v⁄m = 1 / m⁄v = 1⁄p
where p is the mass density. Thus, if p1 > p2, the relation between the specific volumes v1 and v2
will be represented by v1 < v2.

18. A beaker is filled with a liquid up to the mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific weight of the liquid will be

a) 6:5 kN = m3
b) 6:6 kN = m3
c) 6:7 kN = m3
d) 6:8 kN = m3

Answer: a

Explanation: Specific weight(γ) is defined as the weight(w) per unit volume(V ), i.e.,
γ = w⁄V
Thus, γ = 6:5 ⁄10-3 N ⁄ m3 = 6:5 kN/m3.

19. A beaker is filled with a liquid up to the mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific gravity of the liquid will be

a) 0.65
b) 0.66
c) 0.67
d) 0.68
Answer: b

Explanation: Specific gravity(S) of a liquid is defined as the ratio of the density of the liquid(pl) to that of water(pw). Thus, S = 0:66.

20. A beaker is filled with a liquid up to the mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific volume of the liquid will be

a) 1 l =kg
b) 1:5 l =kg
c) 2 l =kg
d) 2:5 l =kg

Answer: b

Explanation: Specific volume(v) is defined as the volume(V ) per unit mass(m).

21). Calculate the specific weight and weight of 20dm3 of petrol of specific gravity 0.6.

a) 5886, 117.2
b) 5886, 234.2
c) 11772, 117.2
d) None of the mentioned

Answer: a

Explanation: Specific weight = density × acceleration due to gravity

=.6 × 1000 × 9.81 = 5886N/m3

Weight = volume × specific weight

= 5886 × 0.02 = 117.2N.

22). If 200m3 of fluid has a weight of 1060N measured on the planet having acceleration due to gravity 6.625m/s2, what will be it’s specific volume?

a) 0.8
b) 0.7
c) 0.9
d) 0.5

Answer: a

Explanation: Specific weight = Weight/volume

= (Mass × acceleration due to gravity)/volume

= density × acceleration due to gravity

= 1/(specific volume × acceleration due to gravity)

Specific volume=1060/(200 × 6.625).

23). For an incompressible fluid does density vary with temperature and pressure?

a) It varies for all temperature and pressure range
b) It remains constant
c) It varies only for lower values of temperature and pressure
d) It varies only for higher values of temperature and pressure

Answer: b

Explanation: For an incompressible fluid, the change in density is negligible. Thus it does not change with temperature and pressure.

24). Specific gravity is what kind of property?

a) Intensive
b) Extensive
c) None of the mentioned
d) It depends on external conditions

Answer: a

Explanation: Specific gravity is an extensive kind of property. It is independent of the quantity of matter present.

25). If there is a bucket full of oil and bucket full of water and you are asked to lift them, which one of the two will require more effort given that volume of buckets remains same?

a) Oil bucket
b) Water bucket
c) Equal effort will be required to lift both of them
d) None of the mentioned

Answer: b

Explanation: The density of water is more than oil. Hence, its weight for the same volume of oil will also be higher. Therefore, more effort will be required.

26). If the fluid has specific weight of 10N/m3 for a volume of 100dm3 on a planet which is having acceleration due to gravity 20m/s2 , what will be its specific weight on a planet having acceleration due to gravity 4m/s2?

a) 5 N/m3
b) 50 N/m3
c) 2 N/m3
d) 10 N/m3

Answer: c

Explanation: For the same volume, specific weight is directly proportional to acceleration due to gravity Specific weight = 4 × 10/20=2.

27). Should Specific Wieght of incompressible fluid only be taken at STP?

a) Yes, as specific weight may show large variation with temperature and pressure
b) No, it can be taken for any temperature and pressure
c) It should be taken at standard temperature but pressure may be any value
d) It should be taken at standard pressure but temperature may be any value

Answer: b

Explanation: Specific weight is inversely proportional to volume. For an incompressible fluid, variation of volume with temperature and pressure is negligible for practical consideration. Therefore, specific weight remains constant.

28). An instrument with air as fluid was involved in some experiment( specific volume was the characteristic property utilized) which was conducted during day in the desert. Due to some reason experiments couldn’t be conducted during day and had to be conducted during night. However, there were considerable errors in obtained values. What might be the reason for these errors?

a) It was human error
b) It was instrumental error
c) Error was due to the fact that experiment was conducted at night
d) None of the mentioned

Answer: c

Explanation: In Desert areas, the temperature at night is considerably lower than at day. Due to this air contracts at night. Hence, its specific volume changes. As specific volume was characteristic property utilized, results obtained showed error due to change in specific volume.

29). A stone weighed 177 N on earth. It was dropped into oil of specific gravity 0.8 on a planet whose acceleration due to gravity is 5m/s2. It displaced oil having weight of 100N. What was the volume of oil displaced by the stone?

a) 25 Litres
b) 15 Litres
c) 25 m3
d) None of the mentioned

Answer: a

Explanation: Volume displaced=oil displaced/(specific gravity × water density × acceleration due to gravity )=100/ (0.8 × 1000 × 5).

30). An compressible fluid’s specific gravity was measured on earth, on a planet having acceleration due to gravity 5.5 times that of earth, and in space at STP. Where will it be having highest value?

a) on the earth
b) on the planet
c) in the space
d) it will be constant everywhere

Answer: d

Explanation: Specific gravity is characteristic property of fluid and is independent of external conditions.

31). Water flows between two plates of which the upper one is stationary and the lower one is moving with a velocity V. What will be the velocity of the fluid in contact with the upper plate?

a) V
b) N ⁄ 2
c) 2V
d) 0

Answer: d

Explanation: According to the No-Slip condition, the relative velocity between the plate and the fluid in contact with it must be zero. Thus, the velocity of the fluid in contact with the upper plate is 0 and that with the lower plate is V.

32). The viscous force the relative motion between the adjacent layers of a fluid in motion.
Which one of the flowing fits best in the sentence?

a) opposes
b) never affects
c) facilitates
d) may effect under certain conditions

Answer: a

Explanation: Viscosity is the internal friction of a fluid in motion. It is the property by the virtue of which the relative motion between two adjacent fluid layers is opposed.

33). The viscosity of a fluid in motion is 1 Poise. What will be it’s viscosity (in Poise) when the fluid is at rest?

a) 0
b) 0.5
c) 1
d) 2

Answer: c

Explanation: Viscosity is the property of a fluid and is constant for a given fluid under given conditions, irrespective of the fact whether the fluid is at rest or in motion.

34). Which of the following correctly states how the viscosities of a liquid and a gas will change with temperature?

a) Viscosity increases with the increase in temperature of a liquid and decreases with the increase in temperature of a gas
b) Viscosity increases with the increase in temperature of a liquid and increases with the increase in temperature of a gas
c) Viscosity decreases with the increase in temperature of a liquid and decreases with the increase in temperature of a gas
d) Viscosity decreases with the increase in temperature of a liquid and increases with the increase in temperature of a gas

Answer: a

Explanation: The viscosity of a liquid is due to the cohesion between it’s molecules. With the increase in temperature of a liquid, cohesion increases, leading to the rise in viscosity. Viscosity of a gas is due to the momentum transfer between it’s molecules. With the increase in the temperature of a liquid, molecular motion increases, leading to a fall in viscosity.

35). Which one of the following is not a unit of dynamic viscosity?

a) Pa-s
b) N-s/m2
c) Poise
d) Stokes

Answer: d 

Explanation:

SI unit of μ is N-s/m2 = Pa-s and CGS unit of μ is dyne-s/cm2. 1 Poise= 1 dyne-s/cm2 and 1 Stokes= 1 cm2/s. Thus, Stokes is not a unit of μ, rather it is a unit of kinematic viscosity υ.

36). Which of the following is a unit of dynamic viscosity?

a) [M1L1T-1].
b) [M1 L-1 T-1].
c) [M1 L-2 T-2].
d) [M1 L-2 T-2].

37). Which one of the following is the CGS unit of dynamic viscosity?

a) Stokes
b) Pa-s
c) m2/s
d) Poise

Answer: d

Explanation:  CGS unit of μ is = dyne-s/cm2. 1 Poise= 1 dyne-s/cm2 and 1 Stokes= 1 cm2/s. Thus, the CGS unit of μ will be Poise. Stokes is the CGS unit of kinematic viscosity.

38). The dynamic viscosity of a fluid is 1 Poise. What should one multiply to it to get the answer in N-s/m2?

a) 0.1
b) 1
c) 10
d) 100

Answer: a

39). Which of the following is a unit of kinematic viscosity?

a) Stokes
b) Pa-s
c) m2=s
d) Poise

Answer: a

Explanation:

Thus, the unit of ν is cm2/s = Stokes Poise is the unit of dynamic viscosity.
1 Poise = 1 dyne-s/cm2

40). Which of the following is the dimension of kinematic viscosity?

a) [L1T-1].
b) [L1T-2].
c) [L2 T-1].
d) [L2 T-2].

Answer: c

41). The kinematic viscosity of a fluid is 0.1 Stokes. What will be the value is m2/s?

a) 10-2
b) 10-3
c) 10-4
d) 10-5

Answer: d

Explanation: 1Stokes = 1cm2/s = 10-4m2/s Therefore, 0.1Stokes = 10-1cm2/s = 10-5m2/s.

42). The shear stress at a point in a liquid is found to be 0.03 N/m2. The velocity gradient at the point is 0.15 s-1. What will be it’s viscosity (in Poise)?

a) 20
b) 2
c) 0.2
d) 0.5

Answer: b

43). The space between two plates (20cm*20cm*1cm), 1 cm apart, is filled with a liquid of viscosity 1 Poise. The upper plate is dragged to the right with a force of 5N keeping the lower plate stationary.

What will be the velocity in m/s of flow at a point 0.5 cm below the lower surface of the upper plate if linear velocity profile is assumed for the flow?

a) 1.25
b) 2.5
c) 12.5
d) 0.25

Answer: c

44. Two horizontal plates placed 250mm have oil of viscosity 20 poises. Calculate the shear stress in oil if the upper plate is moved with velocity of 1250mm/s.
a) 20 N/m2
b) 2 N/m2
c) 10 N/m2
d) None of the mentioned

Answer:c

Explanation: Shear Stress = Viscosity * Velocity Gradient
= 20/10 × 1.25/0.25
= 10 N/m2.

45. The kinematic viscosity of oil of specific gravity .8 is .0005 .This oil is used for lubrication of shaft of diameter .4 m and rotates at 190 rpm. Calculate the power lost in the bearing for a sleeve length of 90mm. The thickness of the oil film is 1.5mm.

a) 477.65 Watts
b) 955.31 Watts
c) 238.83 Watts
d) None of the mentioned

Answer: a

Explanation:

Power lost = torque × angular velocity
= force × radius × angular velocity

= shear stress × area × radius × angular velocity

Shear Stress = viscosity × velocity gradient

Power lost = 0.0005 × 0.8 × 1000 × 2 × 3.142 × 190/60 × 0.2 × 3.142 × 0.23 × 190/60
= 477.65 Watts.

46. Find the kinematic viscosity of oil having density 1962 g/m3. the force experienced for area of 20 m2 is 4.904 kN and velocity of gradient at that point is 0.2/s.

a) 0.625
b) 1.25
c) 2.5
d) None of the mentioned

Answer: a

Explanation: kinematic viscosity = dynamic viscosity / density
= (shear stress × density)/velocity gradient
= (4904 × 1962)/(20 × 0.2)
= .625.

47. The velocity distribution for fluid flow over a flat plate is given by u=2y-6y2 in which u is the velocity in metre per second at a distance of y metre above the plate. Determine the shear stress at y=0.15m.Take dynamic viscosity of fluid as 8.6 poise.

a) 0.172 N/m2
b) 0.344 N/m2
c) 0.086 N/m2
d) None of the mentioned

Answer: a

Explanation: for y = 0.15m, velocity gradient = 0.2

viscosity= shear stress/velocity gradient

shear stress = 0.86 × 0.2 = 0.172N/m2.

48. In which types of fluids it is observed that momentum transfer dominates cohesive forces with increase in temperature and hence viscosity increases
a) Gases
b) Liquids
c) Solids
d) None of the mentioned

Answer: a

Explanation: It is the characteristic property of gases that show an increase in viscosity with an increase in temperature.

49. What is the characteristic variation shown by the thixotropic fluids in their shear stress vs. rate of shear strain graph?

a) shear stress increases with increase in rate of shear strain
b) shear stress decreases with increase in rate of shear strain
c) shear stress shows variation only after a definite shear stress is reached
d) shear stress has decreasing constant and then variation relationship with rate of shear strain

Answer: c

Explanation: Thixotropic fluid show a Non-Newtonian variation for shear stress vs. rate of shear strain graph after a characteristic limiting value of shear stress is reached.

50. What happens to viscosity in the case of incompressible fluids as temperature is increased?

a) It remains constant
b) It increases
c) It decreases
d) None of the mentioned

Answer: c

Explanation: In case of incompressible fluids, cohesive forces govern the viscosity. As temperature increases the cohesive forces between fluid molecules decreases due to increase in molecular agitation. Hence, as a result, viscosity decreases.

51. If a fluid, which has a constant specific gravity, is taken to a planet where acceleration due to gravity is 3 times compared to its value on earth, what will happen to its kinematic viscosity.

a) It increases
b) It decreases
c) It remains constant
d) None of the above

Answer: c

Explanation: Kinematic viscosity depends on density and dynamic viscosity. Both, density and dynamic viscosity, are independent of acceleration due to gravity. Therefore, kinematic viscosity is independent of acceleration due to gravity.

52. In liquids in order to measure the viscosity of fluid experimentally we consider the variation of shear stress with respect to what property?

a) strain
b) shear strain
c) rate of shear strain
d) none of the mentioned

Answer: c

Explanation: By definition, viscosity is shear stress per unit ‘rate of shear strain’.

53. For a compressible fluid the kinematic viscosity is affected by temperature and pressure variation.

a) True
b) False

Answer: a

Explanation: Viscosity shows variation for change in temperature and pressure for compressible fluids. Hence, kinematic viscosity is affected by temperature and pressure variation.

54. Which of the following statement is true about vapor pressure of a liquid?

a) Vapor pressure is closely related to molecular activity and temperature of the liquid
b) Vapor pressure is closely related to molecular activity but independent of the temperature of the liquid
c) Vapor pressure is not affected by molecular activity and temperature of the liquid
d) Vapor pressure is not affected by molecular activity and is independent of the temperature of the liquid

Answer: a

Explanation: The vapor pressure of a liquid at a given temperature is given by the pressure ex-erted by the saturated vapor on the liquid surface. When the vapor is saturated, an equilibrium exists between the liquid and the vapor phases. The number of molecules leaving the liquid surface is equal to the number of molecules entering the liquid surface. Hence, it is obvious that vapor pressure will be related to molecular activity and consequently to temperature. With the increase in temperature molecular activity increases as a result of which vapor pressure increases.

55. Which of the following equation correctly depicts the relation between the vapor pressure of a liquid and it’s temperature?

a) Vapor pressure increases linearly with the increase in temperature of the liquid
b) Vapor pressure increases slightly with the increase in temperature of the liquid at low temperatures and the rate of increase goes high at higher temperatures
c) Vapor pressure increases rapidly with the increase in temperature of the liquid at low temperatures and the rate of increase goes low at higher temperatures
d) Vapor pressure remains unchanged with the increase in temperature of the liquid

Answer: b

Explanation: Vapor pressure is closely related to molecular activity which is in turn dependant on the temperature of the liquid. With the increase in temperature molecular activity of a vapor increases slowly at first and then rapidly. Similar is the nature of variaion of vapor pressure.

56. Which of the following is the condition for the boiling of a liquid?

a) Absolute pressure of a liquid must be greater than or equal to it’s vapor pressure
b) Absolute pressure of a liquid must be less than or equal to it’s vapor pressure
c) Absolute pressure of a liquid must be equal to it’s vapor pressure
d) Absolute pressure of a liquid must be greater than it’s vapor pressure

Answer: b

Explanation: As the absolute pressure of a liquid goes below its vapor pressure, the formation of vapor bubbles starts. Thus, for boiling to start, the absolute pressure of a liquid must be less than or equal to its vapor pressure.

57. Which of the following machines have the possibility of cavitation?

a) Reaction turbines and centrifugal pumps
b) Reaction turbines and reciprocating pumps
c) Impulse turbines and centrifugal pumps
d) Impulse turbines and reciprocating pumps

Answer: a

Explanation: Cavitation occurs whenever absolute pressure of a liquid drops below it’s vapor pressure. Dropping of pressure is observed mainly in reaction turbines and centrifugal pumps.

58. The three liquids 1, 2, and 3 with vapor pressures V1, V2 and V3 respectively, are kept under same pressure. If V1 > V2 > V3, which liquid will start boiling early?

a) liquid 1
b) liquid 2
c) liquid 3
d) they will start boiling at the same time

Answer: a

Explanation: A liquid starts to boil whenever it’s absolute pressure drops below it’s vapor pressure. Thus, the absolute pressure of liquid 1 will drop early, as a result it’ll start boiling early.

59. Equal amount of a particular liquid is poured into three similar containers, namely 1, 2 and 3, at a temperature of T1, T2 and T3 respectively. If T1 < T2 < T3, the liquid in which container will have the highest vapor pressure?

a) container 1
b) container 2
c) container 3
d) the vapor pressure of the liquid will remain the same irrespective of it’s temperature

Answer: c

Explanation: Higher the temperature, higher is the molecular activity, and consequently, higher is the vapor pressure of a given liquid. Since container 3 is at the highest temperature, the liquid in it will have the highest vapor pressure.

60. The absolute pressure of a water is 0.5kN above it’s vapor pressure. If it flows with a velocity of 1m/s, what will be the value of Cavitation Number describing the flow induced boiling?

a) 0.25
b) 0.5
c) 1
d) 2

Answer: c

61. Which of the following is correct regarding the formation and collapse of vapor bubbles in a liquid?

a) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes above the bubble pressure
b) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
c) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
d) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes above the bubble pressure

Answer: d

Explanation: Whenever the absolute pressure of a fluid drops below its vapor pressure, bubble formation starts. Again, when the fluid pressure goes above the bubble pressure, it’ll collapse. This is how cavitation formation takes place.

62.) Which one of the following is the correct relation between compressibility β and Bulk Modulus k

a) β = k
b) β = 1/k
c) β = 2k
d) β = k/2

Answer: b

Explanation: Compressibility β of a liquid is deβned as the ratio of volumetric strain to the compressive stress while Bulk Modulus is the ratio of compressive stress to volumetric strain. Hence, β = 1/k is the correct relation.

63. Which one of the following is true about Bulk Modulus of elasticity?

a) it is the ratio of compressive stress to volumetric strain
b) it is the ratio of compressive stress to linear strain
c) it is the ratio of tensile stress to volumetric strain
d) it is the ratio of tensile stress to linear strain

Answer: a

Explanation: Bulk Modulus k is related to the compression of a liquid and the decrease in volume per unit volume. It is the ratio of compressive stress to the volumetric strain.

64. The value of the Bulk Modulus of elasticity for an incompressible fluid is

a) zero
b) unity
c) infinity
d) very low

Answer: c

Explanation: k = 1/β, where k= Bulk Modulus of elasticity and β= compressibility. For an incompressible fluid, β=0, thus the value of k will tend to infinity.

65. Three fluids 1, 2 and 3 have Bulk Moduli of k1, k2 and k3 respectively. If k1 > k2 > k3, which liquid will have the highest compressibility?

a) liquid 1
b) liquid 2
c) liquid 3
d) they’ll have equal compressibilities

Answer: c

Explanation: k = 1=β, where k= Bulk Modulus of elasticity and β= compressibility. If k1 > k2 > k3, then β1 < β2 < β3. Thus, liquid 3 will have the highest compressibility.

66. Bulk Modulus, Pressure, Force, Stress – Which one of these won’t have the same unit as the others?

a) Bulk Modulus
b) Pressure
c) Force
d) Stress

Answer: c

Explanation: The SI unit of Bulk Modulus, Pressure and Stress is N/m2 but the unit of Force is N.

67. Which of the following is the dimension of Bulk Modulus?
a) [M1L-1T-1].
b) [M1L-1T-2].
c) [M1L1T-2].
d) [M1L1T-1].

Answer: b

68. Which one of the following is the unit of compressibility?

a) m=N
b) m2=N
c) m3=N
d) it is unitless

Answer: b

Explanation: k = 1/β, where k= Bulk Modulus of elasticity and β= compressibility. Thus the unit of Bulk modulus is N/m2 and the unit of compressibility becomes m2/N.

69. Which of the following is the dimension of compressibility?

a) [M1L1T-2].
b) [M1L1T-1].
c) [M-1L1T-2].
d) [M-1L1T2].

Answer: d

Explanation: k = 1/β, where k = Bulk Modulus of elasticity and β= compressibility and [β] = [1/k] = [M-1L1T2].

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