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UPSC Civil Service Exam Questions - Engineering

Q1:

At the same mean velocity, what is the ratio of head loss per unit length for a sewer pipe flowing full to that for the same pipe flowing half full ?

A 2.0

B 1.7

C 1.0

D 0.6

ANS:A - 2.0

Use the formula:

Hf= flQ^2/12d^5.
Since all other values will be same other than "d"
For 1st condition - headloss =Q^2/d^5 = (A*V)^2/d^5.
For 2nd condition- headloss = (A*v)^2/d^5, where d = d/2.
divide 1 and 2.
So, the answer is 2.