Fluid Mechanics Questions and Answers – Time Required to Empty a Reservoir with Weirs or Notches

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This set of Fluid Mechanics Questions and Answers for Aptitude test focuses on “Time Required to Empty a Reservoir Or a Tank with a Rectangular, Triangular & Cipolletti Weir or Notch”.

1. What is the reduction in crest length due to each end contraction?
a) 0.1H
b) 0.2H
c) 0.15H
d) 0.25H
View Answer

Answer: a
Explanation: Francis through his experiment had derived this empirical relation.
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2. In Francis formula, the effective length is –
a) L-0.2H
b) L-0.4H
c) L-0.3H
d) L-0.1H
View Answer

Answer: a
Explanation: In Francis formula, the effective length is L-0.2H.

3. In Francis empirical expression for discharge, the relation between head of water and discharge is
a) Q is directly proportional to H
b) Q is directly proportional to H1.5
c) Q is directly proportional to H2.5
d) Q is directly proportional to H0.5
View Answer

Answer: b
Explanation: In Francis empirical expression for discharge, the relation between head of water and discharge is Q is directly proportional to H1.5.

4. In Bazin’s formula, the discharge is inversely proportional to the length of weir.
a) True
b) False
View Answer

Answer: b
Explanation: In Bazin’s formula, the discharge is directly proportional to the length of weir.

5. The head of water over a rectangular weir is 38 cm. The length of the crest of the weir end contraction suppressed is 1.3 m. Find the discharge using the Francis formula.
a) 0.56 m3/s
b) 0.75 m3/s
c) 0.85 m3/s
d) 0.69 m3/s
View Answer

Answer: a
Explanation: Q = 1.84*L*H1.5 = 0.56 m3/s.
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6. The head of water over a rectangular weir is 28 cm. The length of the crest of the weir end contraction suppressed is 1.27 m. Find the discharge using the Francis formula.
a) 0.346 m3/s
b) 0.556 m3/s
c) 0.788 m3/s
d) 0.225 m3/s
View Answer

Answer: a
Explanation: Q = m * L * (2*g)0.5 * H1.5
m = ⅔ * Cd
= 0.405 + 0.003/H
= 0.405 + 0.003/0.28
Q = 0.346 m3/s.

7. The head of water over a rectangular weir is 26 cm. The length of the crest of the weir end contraction suppressed is 1.25 m. Find the discharge using the Francis formula.
a) 0.304 m3/s
b) 0.502 m3/s
c) 0.350 m3/s
d) 0.625 m3/s
View Answer

Answer: a
Explanation: Q = 1.84*L*H1.5
= 0.304 m3/s.

8. The head of water over a rectangular weir is 28 cm. The length of the crest of the weir end contraction suppressed is 1.27 m. Find the discharge using the Francis formula.
a) 0.346 m3/s
b) 0.556 m3/s
c) 0.788 m3/s
d) 0.225 m3/s
View Answer

Answer: a
Explanation: Q = m * L * (2*g)0.5 * H1.5
m = ⅔ * Cd
= 0.405 + 0.003/H
= 0.405 + 0.003/0.28
Q = 0.346 m3/s.

9. Find the discharge over a cipolletti weir of length 1.5 m when the head over the weir is 0.85 m. Take Cd = 0.61.
a) 2.12 m3/s
b) 1.25 m3/s
c) 2.5 m3/s
d) 1.5 m3/s
View Answer

Answer: a
Explanation: Q = ⅔ * Cd * L * (2g)0.5 * H1.5
= 2.12 m3/s.

10. Find the discharge over a cipolletti weir of length 1.3 m when the head over the weir is 0.65 m. Take Cd = 0.60.
a) 2.12 m3/s
b) 1.21 m3/s
c) 2.5 m3/s
d) 1.5 m3/s
View Answer

Answer: b
Explanation: Q = ⅔ * Cd * L * (2g)0.5 * H1.5
= 1.21 m3/s.
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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn