How Well You Know About Fluid Mechanics? Trivia Quiz
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How well do you know about fluid mechanics? Fluid mechanics is the branch of physics concerned with the processing of fluid. It is the function of the laws of force and motion to fluids, liquids, and gases. Both liquids and gases are considered fluids for the aim of this branch of science. Fluid mechanics involves a substantial understanding of complex mathematics. Remember to get your certificate once you have completed this quiz.
Questions and Answers
1.
A fluid flows steadily through a pipe with a uniform cross-section area. The density ρ
of the fluid decreases to half its initial value as it flows through the pipe. Choose the
letter of the correct statement about the average velocity V.
A.
V2 equals 2 V1
B.
V2 equals V1/2
C.
V2 equals V1
D.
V2 equals V1/4
E.
V2 equals 4 V1
Correct Answer A. V2 equals 2 V1
Explanation As the density of the fluid decreases to half its initial value, the mass flow rate remains constant since the fluid is flowing steadily. The mass flow rate is given by the product of density, cross-sectional area, and velocity. Since the mass flow rate is constant and the density decreases by half, the velocity must double to maintain the same mass flow rate. Therefore, V2 equals 2 V1.
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2.
Water flows through a pipe and enters a section where the cross-sectional area is
smaller. Viscosity, friction, and gravitational effects are negligible. Choose the letter
of the correct statement about the change in pressure p and average velocity V.
A.
P2 is less than P1 and V2 is less than V1
B.
P2 is less than P1 and V2 is greater than V1
C.
P2 is greater than P1 and V2 is less than V1
D.
P2 is greater than P1 and V2 is greater than V1
Correct Answer B. P2 is less than P1 and V2 is greater than V1
Explanation When water flows through a pipe and enters a section where the cross-sectional area is smaller, the principle of continuity states that the product of the cross-sectional area and the velocity of the fluid remains constant. In this case, the cross-sectional area decreases, which means that the velocity of the water must increase to maintain the constant product. As a result, the average velocity V2 in the smaller section is greater than the average velocity V1 in the larger section. According to Bernoulli's equation, when the velocity of a fluid increases, the pressure decreases. Therefore, the pressure P2 in the smaller section is less than the pressure P1 in the larger section.
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3.
Two fluid jets are pointed at surfaces as shown in the figures below. The fluids are
incompressible, and the effects of gravity can be neglected. The mass flow rate and
the velocity of the jets are identical. The cross-section area of the jets does not
change significantly as the fluid flows. Choose the letter of the correct statement
regarding the horizontal forces.
A.
F1 equals 2 F2
B.
F1 is greater than 0 and F2 equals 0
C.
F1 equals F2/2
D.
F1 equals 0 and F2is greater than 0
E.
F1 equals F2
Correct Answer C. F1 equals F2/2
Explanation The horizontal forces exerted by the fluid jets are equal to each other, with F1 being half of F2. This means that the force exerted by the first jet is half of the force exerted by the second jet.
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4.
Choose the correct statement about pressure in a fluid.
A.
Pressure is a body force.
B.
Pressure acts normal to a surface.
C.
Pressure is a frictional force.
D.
Pressure acts parallel to a surface.
Correct Answer B. Pressure acts normal to a surface.
Explanation Pressure acts normal to a surface means that the force exerted by the fluid is perpendicular to the surface it is acting on. This is because pressure is defined as the force per unit area, and the force is distributed equally in all directions. Therefore, the correct statement is that pressure acts normal to a surface.
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5.
A layer of water is between a stationary surface and a moving plate as shown in two
figures below. The plate velocities in each figure are the same. The water in the
second figure is twice as deep as the water layer in the first figure. The water layer is
laminar. Choose the letter of the correct statement about the forces.
A.
F1 equals 2 F2
B.
F1 equals 4 F2
C.
F1 equals F2/2
D.
F1 equals F2/4
E.
F1 equals F2
Correct Answer A. F1 equals 2 F2
Explanation The correct statement about the forces is that F1 equals 2 F2. This means that the force exerted by the water layer on the stationary surface in the second figure is twice as much as the force exerted in the first figure. This can be attributed to the fact that the water layer in the second figure is twice as deep, resulting in a greater force being exerted on the surface.
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6.
Water flows through two smooth pipes with the same diameter and length as shown
below. The flow rate through the second pipe is twice that through the first pipe.
Both flows are laminar and fully developed. Choose the letter of the statement that is
correct about the pressure drop (pressure difference over the pipe length).
A.
Pipe 1 has the higher pressure drop
B.
Pipe 2 has the higher pressure drop
C.
Pipes 1 and 2 have the same pressure drop
D.
All of the above
E.
None of the above
Correct Answer B. Pipe 2 has the higher pressure drop
Explanation The pressure drop in a pipe is directly proportional to the flow rate. Since the flow rate through the second pipe is twice that through the first pipe, the pressure drop in the second pipe will be higher. Therefore, the correct statement is that Pipe 2 has the higher pressure drop.
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7.
Choose the correct statement about the shear stress in a flow field.
A.
Shear stress is proportional to velocity
B.
Shear stress is proportional to the square of velocity
C.
Shear stress is proportional to the velocity gradient in the direction of flow
D.
Shear stress is proportional to velocity gradient normal to the flow
E.
Shear stress is proportional to the difference in velocity
Correct Answer D. Shear stress is proportional to velocity gradient normal to the flow
Explanation The correct statement about shear stress in a flow field is that it is proportional to the velocity gradient normal to the flow. This means that the shear stress is directly related to the rate at which the velocity changes perpendicular to the direction of flow. As the velocity gradient increases, so does the shear stress. This relationship is important in understanding the behavior of fluids in motion and is used in various engineering applications.
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8.
Water flows through a pipe and enters a section where the cross-sectional area is
larger. Viscosity, friction, and gravitational effects are negligible. Choose the letter of
the correct statement about the change in pressure p and average velocity V.
A.
P2 is less than P1 and V2 is less than V1
B.
P2 is less than P1 and V2 is greater than V1
C.
P2 is greater than P1 and V2 is less than V1
D.
P2 is greater than P1 and V2 is greater than V1
Correct Answer C. P2 is greater than P1 and V2 is less than V1
Explanation When water flows through a pipe and enters a section where the cross-sectional area is larger, according to the given information that viscosity, friction, and gravitational effects are negligible, the Bernoulli's principle can be applied. According to Bernoulli's principle, as the cross-sectional area increases, the velocity of the fluid decreases and the pressure increases. Therefore, P2 is greater than P1 and V2 is less than V1.
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9.
Two very long plates, with a layer of water between them, are pulled in opposite
directions as shown below. There is no imposed pressure gradient in the direction of
flow and the velocities in the water are laminar and due only to the motion of the
plate. Choose the letter that best represents the velocity profile (distribution of the
velocity of the water with distance) inside the fluid.
A.
Profile A
B.
Profile B
C.
Profile C
D.
Profile D
E.
None of the above
Correct Answer A. Profile A
Explanation The correct answer is Profile A because in laminar flow between two plates, the velocity profile is typically parabolic. This means that the velocity is highest at the center of the water layer and decreases towards the plates. Profile A represents this parabolic velocity distribution, with the highest velocity in the middle and lower velocities closer to the plates. Profile B, C, and D do not accurately represent the expected velocity profile in laminar flow between two plates.
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10.
Water flows vertically up through a pipe and enters a section where the cross-sectional area is smaller. Viscosity and pipe friction effects are negligible but
gravitational effects are not negligible. Choose the letter of the correct statement about
the pressure P2 and velocity V2.
A.
P2 equals P1 and V2 equals V1
B.
P2 is greater than P1 and the V2 is greater than V1
C.
P2 is greater than P1 and the V2 is less than V1
D.
P2 is less than P1 and the V2 is greater than V1
E.
P2 is less than P1 and the V2 is less than V1
Correct Answer D. P2 is less than P1 and the V2 is greater than V1
Explanation When water flows vertically up through a pipe and enters a section where the cross-sectional area is smaller, the pressure decreases and the velocity increases. This is because as the cross-sectional area decreases, the same amount of water must flow through a smaller space, leading to an increase in velocity. Additionally, according to Bernoulli's principle, as the velocity increases, the pressure decreases. Therefore, P2 is less than P1 and V2 is greater than V1.
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11.
Find the Reynolds number of a water flow at an average speed of 20ft/s at 60degee F in a 6 in. diameter pipe. If the Reynolds numbers is 2300, what is the maximum speed at which the flow will be in laminar.Take Kinematic viscosity as 1.21*10^-5 sq. ft/s
A.
8.26*10^-5; 0.056 ft/s
B.
8.26*10^5; 0.056 ft/s
C.
8.26*10^-4; 0.56 ft/s
D.
8.26*10^5; 0.56 ft/s
E.
None of the above
Correct Answer B. 8.26*10^5; 0.056 ft/s
Explanation The Reynolds number is a dimensionless quantity that determines the flow regime of a fluid. It is calculated by multiplying the average speed of the flow, the diameter of the pipe, and the kinematic viscosity of the fluid, and then dividing by the dynamic viscosity. In this question, the Reynolds number is given as 2300, which indicates the transition from laminar to turbulent flow. To find the maximum speed at which the flow will be laminar, we need to increase the Reynolds number. By increasing the Reynolds number, the flow will transition to turbulent. Therefore, the correct answer is 8.26*10^5; 0.056 ft/s, as it has the highest Reynolds number and the lowest speed.
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12.
Power is ..........
A.
Force times area
B.
Work times area
C.
Force per unit time
D.
Work done per unit time
E.
None of the above
Correct Answer D. Work done per unit time
Explanation The correct answer is "Work done per unit time". Power is a measure of how quickly work is done or energy is transferred. It is calculated by dividing the work done by the time taken. Therefore, power is defined as the rate at which work is done or the rate at which energy is transferred.
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13.
An inverted U-tube is connected across two pipes 1 and 2 carrying fluids as shown in Fig. Calculate the pressure difference between point 1 and 2 (at center of the pipes). Note: the values given in the bracket are sp. gravity of the fluids.
A.
-932N/m
B.
-932N/sq.m
C.
932N/m
D.
932N/sq.m
E.
None of the above
Correct Answer B. -932N/sq.m
Explanation The pressure difference between two points in a fluid can be calculated using the equation: ΔP = ρgh, where ΔP is the pressure difference, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height difference between the two points. In this case, since the U-tube is inverted, the height difference between the two points is negative. Therefore, the pressure difference between point 1 and 2 is negative, indicating that the pressure at point 1 is higher than the pressure at point 2. The correct answer, -932N/sq.m, represents the negative pressure difference between the two points.
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14.
Value of Coefficient of discharge (Cd) for venturi meter
A.
0.095 to 0.098
B.
0.070 to 0.080
C.
0.95 to 0.98
D.
0.60 to 0.65
E.
0.70 to 0.80
Correct Answer C. 0.95 to 0.98
Explanation The value of the coefficient of discharge (Cd) for a venturi meter is typically between 0.95 and 0.98. This coefficient represents the ratio of the actual flow rate to the theoretical flow rate through the venturi meter. A higher Cd value indicates a more accurate measurement. Therefore, a Cd value between 0.95 and 0.98 suggests that the venturi meter is able to provide relatively precise and reliable flow rate measurements.
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15.
Choose the correct answer
A.
Head loss across venturi meter is very high
B.
Head loss across orifice meter is low
C.
Head loss across Flow nozzle is intermediate
D.
All the above are correct
E.
All the above are wrong
Correct Answer C. Head loss across Flow nozzle is intermediate
Explanation The given answer states that the head loss across a Flow nozzle is intermediate. This means that the amount of energy loss due to friction and turbulence in a Flow nozzle is moderate compared to a venturi meter and an orifice meter. In other words, the Flow nozzle causes a moderate decrease in pressure as the fluid flows through it. This explanation provides a clear understanding of the head loss characteristics of a Flow nozzle in comparison to other types of flow meters.
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16.
Fig. A: Fig. B: Fig. C: Fig. D: Fig. E: Fig. F: Fig. A, Fig. B, Fig. C, Fig. D, Fig. E and Fig. F represent some physical phenomenons. Choose the option of correct order.
A.
Capillary rise, Impact of jet, Viscous effect, Surface tension, Buoyancy, Submerged body
Correct Answer C. Surface tension, Capillary rise, Viscous effect, Buoyancy, Impact of jet, Submerged body
Explanation The correct order is Surface tension, Capillary rise, Viscous effect, Buoyancy, Impact of jet, Submerged body. Surface tension is the force that causes the surface of a liquid to behave like a stretched elastic sheet. Capillary rise is the phenomenon where a liquid rises in a narrow tube against the force of gravity. Viscous effect refers to the resistance of a fluid to flow. Buoyancy is the upward force exerted on an object submerged in a fluid. Impact of jet is the force exerted by a fluid jet on a surface it strikes. Submerged body refers to an object partially or fully immersed in a fluid. This order represents the progression of these physical phenomena.
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17.
What is co-efficient of discharge?
A.
Product of Actual and Theoretical discharges
B.
Sum of Actual and Theoretical discharges
C.
Ratio between Actual and Theoretical discharges
D.
Ratio between Theoretical and Actual discharges
E.
None of the above
Correct Answer C. Ratio between Actual and Theoretical discharges
Explanation The coefficient of discharge is a dimensionless quantity that represents the ratio between the actual discharge and the theoretical discharge. It is used to describe the efficiency of a fluid flow system, such as a pipe or a nozzle. A coefficient of discharge greater than 1 indicates that the actual discharge is higher than the theoretical discharge, while a coefficient less than 1 indicates that the actual discharge is lower. The correct answer is "Ratio between Actual and Theoretical discharges."
Explanation The correct answer is the arrangement of the substances from the most rigid to the least rigid. A solid is the most rigid substance, followed by a plastic fluid which has some rigidity but can still flow, then a non-Newtonian fluid which has variable viscosity depending on the applied stress, followed by a Newtonian fluid which has constant viscosity, and finally an ideal fluid which has no viscosity and can flow easily.
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19.
Slim and Chubby persons weigh 70 and 140 kg. Area of their feet is 0.03 sq.m. find the normal stresses (approximate) on their feet.
A.
20 kPa, 40 kPa
B.
21 kPa, 42 kPa
C.
23 kPa, 46 kPa
D.
25 kPa, 50 kPa
E.
50 kPa, 80 kPa
Correct Answer C. 23 kPa, 46 kPa
Explanation The normal stress on an object is given by the formula stress = force/area. In this case, the force is the weight of the person, and the area is the area of their feet. For the slim person, the weight is 70 kg, so the force is 70 kg * 9.8 m/s^2 = 686 N. Dividing this by the area of 0.03 sq.m gives a stress of approximately 22.87 kPa, which can be rounded to 23 kPa. For the chubby person, the weight is 140 kg, so the force is 140 kg * 9.8 m/s^2 = 1372 N. Dividing this by the same area gives a stress of approximately 45.73 kPa, which can be rounded to 46 kPa.
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20.
A manometer is used to measure the pressure in a tank. The fluid used has a specific gravity of 0.85, and the manometer column height is 55 cm, as shown in Fig. If the local atm. pressure is 96kPa, determine the absolute pressure within the tank.
A.
120.65 kPa
B.
100.60 kPa
C.
96.00 kPa
D.
93.58 kPa
E.
None of the above
Correct Answer B. 100.60 kPa
Explanation The manometer measures the difference in pressure between the fluid in the tank and the atmospheric pressure. The height of the fluid column in the manometer is 55 cm. The specific gravity of the fluid is 0.85, which means it is lighter than water. This indicates that the pressure in the tank is greater than the atmospheric pressure. By using the formula P = ρgh, where P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height of the fluid column, we can calculate the pressure in the tank. Plugging in the values, we get P = (0.85)(1000 kg/m^3)(9.81 m/s^2)(0.55 m) = 100.60 kPa. Therefore, the correct answer is 100.60 kPa.