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Notches and Weirs MCQs - Fluid Mechanics

Notches and Weirs MCQs - Fluid Mechanics: This section contains the multiple-choice questions and answers on the fluid mechanics chapter Notches and Weirs. practice these MCQs to learn and enhance the knowledge of Notches and Weirs.

1. What is a notch in fluid mechanics?

1. A tool used to measure fluid velocity
2. A type of flow obstruction
3. A unit of pressure measurement
4. A device to measure fluid viscosity

Answer: B) A type of flow obstruction

Explanation:

A notch is a form of flow obstruction that is used to evaluate the flow rate of liquids. It is made out of a specially created opening in the wall that allows liquid to pass through.

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2. A triangular notch is used to measure:

1. Viscosity
2. Velocity
3. Flow rate
4. Pressure

Answer: C) Flow rate

Explanation:

A triangular notch is specially developed to assess liquid flow rate. The flow rate can be determined using the liquid's height above the bottom of the notch.

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3. Which type of notch or weir has a crest that is significantly wider than the approach channel?

1. V-notch weir
2. Suppressed weir
3. Broad-crested weir
4. Submerged weir

Answer: C) Broad-crested weir

Explanation:

A broad-crested weir has a crest that is far greater than the approach channel. This design makes it easier for the weir to handle large flow rates.

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4. A Cipoletti weir is classified as a type of:

1. Trapezoidal weir
2. Broad-crested weir
3. V-notch weir
4. Triangular weir

Answer: A) Trapezoidal weir

Explanation:

A Cipoletti weir is a specific design of a Trapezoidal weir that includes notches in the crest to improve flow behavior and measurement accuracy.

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5. The discharge over a rectangular weir is calculated using the formula:

1. Q = kH^n
2. Q = Cd × A × √2g × H^3/2
3. Q = A × V
4. Q = Cd × A × H^2

Answer: B) Q = Cd × A × √2g × H^3/2

Explanation:

The discharge over a rectangular weir is calculated using the Francis formula, Q = Cd × A × √2g × H^3/2, where Cd is the coefficient of discharge, A is the cross-sectional area of flow, g is the acceleration due to gravity, and H is the head of water above the weir crest.

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6. In the equation Q = Cd × A × √2g × H^3/2, what does 'A' represent?

1. Acceleration due to gravity
2. Coefficient of discharge
3. Cross-sectional area of flow
4. Head of water above the weir crest

Answer: C) Cross-sectional area of flow

Explanation:

'A' represents the cross-sectional area of flow over the weir. It is one of the factors that determine the flow rate through the weir.

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7. What is the primary factor that determines the discharge over a triangular notch or weir?

1. Base width of the triangle
2. Perimeter of the triangle
3. Height of the triangle
4. Apex angle of the triangle

Answer: C) Height of the triangle

Explanation:

The height of the triangle that results from the notch determines the discharge over a triangular notch or weir. The flow rate is influenced by the height of the liquid above the apex of the triangle.

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8. What effect does increase approach velocity have on discharge over a triangular weir?

1. It increases the discharge
2. It changes the shape of the velocity profile
3. It does not affect the discharge
4. It decreases the discharge

Answer: A) It increases the discharge

Explanation:

As approach velocity increases, kinetic energy increases, resulting in increasing discharge over the triangle weir. The flow rate measurement is influenced by the kinetic energy of the approaching flow.

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9. A triangular notch with an apex angle of 60 degrees is used to measure the flow rate. The head of water above the apex is 0.2 meters. Calculate the discharge over the notch.

1. 0.0132 m³/s
2. 0.0264 m³/s
3. 0.0528 m³/s
4. 0.0792 m³/s

Answer: B) 0.0264 m³/s

Explanation:

The formula for discharge over a triangular notch is given by:

Q=1.42×b×h5/2
Where:
Q = Discharge
b = Base width of the notch
h = Head of water above the apex
Given that the apex angle is 60 degrees, the base width is
b=2×htan(30∘).
Plugging in the values:
b=2×0.2×tan(30∘)≈0.2309 m
Q=1.42×0.2309×0.25/2
≈0.0264 m³/s

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10. What is the main advantage of the use of a triangular notch or weir for flow measurement over a rectangular notch or weir?

1. Triangular notches are easier to fabricate
2. Triangular notches can handle higher flow rates
3. Triangular notches have a wider range of applications
4. Triangular notches provide better accuracy at low flow rates

Answer: D) Triangular notches provide better accuracy at low flow rates.

Explanation:

Due to their unique shape, triangular notches are more accurate than rectangular notches at measuring low flow rates. In the low flow system, where rectangular notches may have constraints, the triangular design improves measurement accuracy.

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11. What feature of triangular notches makes them so effective at measuring low flow rates?

1. Their narrower crest width
2. Their smoother flow transition
3. Their increased discharge coefficient
4. Their larger crest height

Answer: A) Their narrower crest width

Explanation:

Because triangular notches have a narrower crest width than rectangular notches, they provide a better response in properly measuring low flow rates by improving the measurement's sensitivity to small changes in water level.

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12. When dealing with irregular flow patterns, why could a triangular weir be favored over a rectangular weir?

1. Triangular weirs are less affected by irregular flow
2. Triangular weirs can handle higher flow rates
3. Triangular weirs have better visibility
4. Triangular weirs are less expensive to install

Answer: A) Triangular weirs are less affected by irregular flow.

Explanation:

The triangular design helps the flow to transition more smoothly over the crest, reducing the impact of turbulence and imperfections in the flow and leading to more accurate measurements.

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13. In a trapezoidal notch, the flow rate is directly proportional to:

1. The average of the base and top widths
2. The height of the notch
3. The width of the base
4. The difference between the base and top widths

Answer: B) The height of the notch

Explanation:

The height of a trapezoidal notch determines the flow rate through it. The height increases as the flow rate increases.

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14. The equation Q = k × L × H^n is used to calculate the discharge over a trapezoidal notch. What does 'L' represent?

1. Length of the bottom base
2. Length of the side slope
3. Length of the top base
4. Average length of the bases

Answer: D) Average length of the bases

Explanation:

In the trapezoidal notch equation, 'L' denotes the average length of the trapezoid's top and bottom bases. It is a length that is used in the calculation.

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15. The discharge over a stepped notch is affected by:

1. Only the channel width
2. Only the step height
3. Both the step height and the channel width
4. Neither the step height nor the channel width

Answer: C) Both the step height and the channel width

Explanation:

Both the step height and the channel width influence the discharge across a stepped notch. These parameters, along with other factors such as the approach flow conditions, affect the flow rate calculation.

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16. Why is the velocity of approach idea essential in fluid mechanics?

1. It influences the fluid's viscosity
2. It determines the fluid's temperature
3. It impacts the pressure distribution on surfaces
4. It affects the density of the fluid

Answer: C) It impacts the pressure distribution on surfaces

Explanation:

When a fluid flows over an obstruction, the velocity of the approach changes the pressure distribution on the surface. It plays a role in designing structures that can withstand fluid forces.

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17. How is the approach of velocity usually calculated?

1. By measuring the fluid's density
2. By using a Pitot tube
3. By determining the fluid's specific gravity
4. By calculating the fluid's viscosity

Answer: B) By using a Pitot tube

Explanation:

A Pitot tube is widely used to determine the velocity of the approach. It operates by aligning the open end of the tube with the fluid's velocity direction, allowing pressure measurements to be transformed into velocity values.

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18. What differentiates a Cipolletti weir from other types of weirs?

1. It is complex to install and operate
2. It can handle only high flow rates
3. It is not affected by variations in water level
4. It can handle a wide range of flow rates

Answer: D) It can handle a wide range of flow rates

Explanation:

One of the key advantages of a Cipolletti weir is its ability to handle a wide range of flow rates, making it flexible to a variety of flow circumstances.

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