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A rectangular open channel of 6 m width is carrying discharge of 20 m3/s . Consider the acceleration due to gravity as 9.81m/s2 and assume water as incompressible and inviscid. The depth of flow in the channel at which the specific energy of the flowing water is minimum for given discharge will then be: 
  • a)
    2.56 m  
  • b)
    0.82 m
  • c)
    1.04 m
  • d)
    3.18 m 
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
A rectangular open channel of 6 m width is carrying discharge of 20 m3...
The specific energy of flowing water in an open channel is the sum of its elevation head and velocity head. The elevation head represents the potential energy of the water, while the velocity head represents the kinetic energy of the water.

To find the depth of flow at which the specific energy is minimum, we need to calculate the specific energy for different depths and determine the depth that gives the lowest value.

Given data:
Width of the channel (b) = 6 m
Discharge (Q) = 20 m3/s
Acceleration due to gravity (g) = 9.81 m/s2

The specific energy (E) is given by the equation:
E = (y + V^2 / 2g) + z

Where:
y = depth of flow
V = velocity of flow
z = elevation of the channel bottom

To find the depth of flow at which the specific energy is minimum, we will differentiate the specific energy equation with respect to y and equate it to zero.

Calculations:
1. Velocity of flow (V):
Q = b * y * V
20 = 6 * y * V
V = 20 / (6y)

2. Elevation of the channel bottom (z):
Assuming the channel bottom is at a constant elevation, z can be considered zero.

3. Specific energy equation:
E = (y + V^2 / 2g) + z

Substituting the values of V and z into the equation:
E = (y + (20 / (6y))^2 / 2 * 9.81) + 0
E = (y + 100 / (3y^2)) + 0
E = (3y^3 + 100) / (3y^2)

To find the minimum specific energy, we differentiate E with respect to y and equate it to zero:
dE/dy = (9y^2 - 200) / (3y^3) = 0

Solving the equation:
9y^2 - 200 = 0
y^2 = 200 / 9
y = √(200 / 9)
y ≈ 1.04 m

Therefore, the depth of flow in the channel at which the specific energy of the flowing water is minimum for the given discharge is approximately 1.04 m. Hence, the correct answer is option C.
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Community Answer
A rectangular open channel of 6 m width is carrying discharge of 20 m3...
Given : 
Width of channel, (B) = 6 m
Discharge of channel, (Q) = 20 m3 /sec


∴ Depth of flow at which SE will be minimum is critical depth and is value 1.04 m.  
Hence, the correct option is (C). 
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A rectangular open channel of 6 m width is carrying discharge of 20 m3/s . Consider the acceleration due to gravity as 9.81m/s2 and assume water as incompressible and inviscid. The depth of flow in the channel at which the specific energy of the flowing water is minimum for given discharge will then be:a)2.56 m b)0.82 mc)1.04 md)3.18 mCorrect answer is option 'C'. Can you explain this answer?
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A rectangular open channel of 6 m width is carrying discharge of 20 m3/s . Consider the acceleration due to gravity as 9.81m/s2 and assume water as incompressible and inviscid. The depth of flow in the channel at which the specific energy of the flowing water is minimum for given discharge will then be:a)2.56 m b)0.82 mc)1.04 md)3.18 mCorrect answer is option 'C'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about A rectangular open channel of 6 m width is carrying discharge of 20 m3/s . Consider the acceleration due to gravity as 9.81m/s2 and assume water as incompressible and inviscid. The depth of flow in the channel at which the specific energy of the flowing water is minimum for given discharge will then be:a)2.56 m b)0.82 mc)1.04 md)3.18 mCorrect answer is option 'C'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A rectangular open channel of 6 m width is carrying discharge of 20 m3/s . Consider the acceleration due to gravity as 9.81m/s2 and assume water as incompressible and inviscid. The depth of flow in the channel at which the specific energy of the flowing water is minimum for given discharge will then be:a)2.56 m b)0.82 mc)1.04 md)3.18 mCorrect answer is option 'C'. Can you explain this answer?.
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