This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Loss of Energy in Pipes”.

1. Which one of the following is a major loss?

a) frictional loss

b) shock loss

c) entry loss

d) exit loss

View Answer

Explanation: The major loss for the flflow through the pipes is due to the frictional resistance between adjacent fluid layers sliding over each other. All other losses are considered to be minor losses.

2. Which property of the fluid accounts for the major losses in pipes?

a) density

b) specific gravity

c) viscosity

d) compressibility

View Answer

Explanation: The major loss for the flow through the pipes is due to the frictional resistance between adjacent fluid layers sliding over each other. This resistance arises due to the presence of viscous property of the fluid.

3. The frictional resistance for fluids in motion is

a) proportional to the velocity in laminar flow and to the square of the velocity in turbulent flow

b) proportional to the square of the velocity in laminar flow and to the velocity in turbulent flow

c) proportional to the velocity in both laminar flow and turbulent flow

d) proportional to the square of the velocity in both laminar flow and turbulent flow

View Answer

Explanation: According to the laws of fluid friction, r

_{f}/ v (for steady streamline flow) and r

_{f}/ v2(for turbulent flow), where rf is the frictional resistance and v is the velocity of flow.

4. The frictional resistance for fluids in motion is

a) dependent on the pressure for both laminar and turbulent flows

b) independent of the pressure for both laminar and turbulent flows

c) dependent on the pressure for laminar flow and independent of the pressure for turbulent flow

d) independent of the pressure for laminar flow and dependent on the pressure for turbulent flow

View Answer

Explanation: According to the laws of fluid friction, the frictional resistance is independent of the pressure for both laminar and turbulent flows.

5. The frictional resistance for fluids in motion is

a) inversely proportional to the square of the surface area of contact

b) inversely proportional to the surface area of contact

c) proportional to the square of the surface area of contact

d) proportional to the surface area of contact

View Answer

Explanation: According to the laws of fluid friction, the frictional resistance is proportional to the surface area of contact for both laminar and turbulent flows.

6. The frictional resistance for fluids in motion varies

a) slightly with temperature for both laminar and turbulent flows

b) considerably with temperature for both laminar and turbulent flows

c) slightly with temperature for laminar flow and considerably with temperature for turbulent flow

d) considerably with temperature for laminar flow and slightly with temperature for turbulent flow

View Answer

Explanation: According to the laws of fluid friction, the frictional resistance for fluids in motion varies considerably with temperature for laminar flow and slightly with temperature for turbulent flow.

7. Which one of the follflowing is correct?

a) the frictional resistance depends on the nature of the surface area of contact

b) the frictional resistance is independent of the nature of the surface area of contact

c) the frictional resistance depends on the nature of the surface area of contact for laminar flows but is independent of the nature of the surface area of contact for turbulent flows

d) the frictional resistance is independent of the nature of the surface area of contact for laminar flows but depends on the nature of the surface area of contact for turbulent flows

View Answer

Explanation: According to the laws of fluid friction, the frictional resistance is independent of the nature of the surface area of contact for laminar flows but depends on the nature of the surface area of contact for turbulent flows.

8. Which one of the follflowing is correct?

a) the frictional resistance is always dependent on the nature of the surface area of contact

b) the frictional resistance is always independent of the nature of the surface area of contact

c) the frictional resistance is dependent on the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

d) the frictional resistance is independent of the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

View Answer

Explanation: Frictional resistance is dependent on the nature of the surface area of contact. But, when the liquid flows at a velocity less than the critical velocity, a thin stationary film of the liquid is formed on the supporting surface. Hence, the frictional resistance becomes independent of the nature of the surface of contact.

9. Which one of the follflowing is correct?

a) Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes and open channels

b) Chezy’s formula is generally used for head loss in flow through both pipes and open channels

c) Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes and Chezy’s formula for open channels

d) Chezy’s formula is generally used for head loss in flow through both pipes and Darcy-Weisbach’s formula for open channels

View Answer

Explanation: Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes as it takes into consideration the flow velocity whereas Chezy’s formula is used for open channels as it considers the pressure difference.

10. A liquid flows through pipes 1 and 2 with the same flow velocity. If the ratio of their pipe diameters d_{1} : d_{2} be 3:2, what will be the ratio of the head loss in the two pipes?

a) 3:2

b) 9:4

c) 2:3

d) 4:9

View Answer

Explanation: According to Darcy-Weisbach’s formula,

whereh

_{f}is the head loss in the pipe, f is the co-efficient of friction, L is the length, D is the diameter and V is the flow velocity. Thus, h

_{f1}: h

_{f2}= D

_{2}: D

_{1}= 2 : 3.

11. A liquid flowss through two similar pipes 1 and 2. If the ratio of their flow velocities v1 : v2 be 2:3, what will be the ratio of the head loss in the two pipes?

a) 3:2

b) 9:4

c) 2:3

d) 4:9

View Answer

Explanation: According to Darcy-Weisbach’s formula,

where h

_{f}is the head loss in the pipe, f is the co-efficient of friction, L is the length, D is the diameter and V is the flow velocity. Thus, h

_{f1}: h

_{f2}= v1 : v2 = 4 : 9.

12. A liquid flows with the same velocity through two pipes 1 and 2 having the same diameter. If the length of the second pipe be twice that of the first pipe, what should be the ratio of the head loss in the two pipes?

a) 1:2

b) 2:1

c) 1:4

d) 4:1

View Answer

Explanation: According to Darcy-Weisbach’s formula,

where h

_{f}is the head loss in the pipe, f is the co-efficient of friction, L is the length, D is the diameter and V is the flow velocity. Thus, h

_{f1}: h

_{f2}= L1 : L2 = 1 : 2.

13. The head loss at the entrance of the pipe is that at it’s exit

a) equal to

b) half

c) twice

d) four times

View Answer

Explanation: According to Darcy-Weisbach’s formula,

h

_{i}= o.5v

^{2}/ 2g and ho = v

^{2}/ 2g, where h

_{i}is the head loss at pipe entrance, h

_{o}is the head loss at pipe exit and v is the flow velocity. Thus h

_{i}= 0.5h

_{o}.

14. On which of the factors does the co-efficent of bend in a pipe depend?

a) angle of bend and radius of curvature of the bend

b) angle of bend and radius of the pipe

c) radius of curvature of the bend and pipe

d) radius of curvature of the bend and pipe and angle of bend

View Answer

Explanation: The co-efficent of bend in a pipe depends on all the three parameters – radius of curvature of the bend, diameter (radius) of the pipe and angle of bend.

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