# Civil Engineering - UPSC Civil Service Exam Questions - Discussion

Discussion Forum : UPSC Civil Service Exam Questions - Section 27 (Q.No. 38)

38.

Two reservoirs at different surface elevations are connected by a set of two pipes A and B of same diameter and length in parallel. If the friction factor of A is 4 times that of the pipe B, what is the ratio of the discharge in A to that in B ?

Discussion:

6 comments Page 1 of 1.
Rahul said:
1 year ago

Option D is correct.

H = flQ^2/12.1d^5.

Q1/Q2 = √ f2/f1.

= 1/2 or 0.5.

H = flQ^2/12.1d^5.

Q1/Q2 = √ f2/f1.

= 1/2 or 0.5.

Apcivilian said:
2 years ago

Yes, the right answer is D.

Karthika.c said:
7 years ago

@Santu ans is 2 not 0.5.

f2/f1=1/2.

Q=A/V.

Q1/Q2=4 (v1/v2)^2.

Then elaborate Q1/Q2.

I.e (A1*v1)/(A2/v2)=4 (v1/V2)^then cancel v1/v2 on both sites.

We get,

Then A1/A2=4 [v1/v2].

Hence v1/v2=root of f2/f1 = 1/2.

So, the ans is A1/A2 = 4 * (1/2).

We get the ans 2. So answer c is correct.

f2/f1=1/2.

Q=A/V.

Q1/Q2=4 (v1/v2)^2.

Then elaborate Q1/Q2.

I.e (A1*v1)/(A2/v2)=4 (v1/V2)^then cancel v1/v2 on both sites.

We get,

Then A1/A2=4 [v1/v2].

Hence v1/v2=root of f2/f1 = 1/2.

So, the ans is A1/A2 = 4 * (1/2).

We get the ans 2. So answer c is correct.

Chhaya said:
7 years ago

Right @Santu Naskar.

Santu naskar said:
7 years ago

Answer is D.

If two pipe in parallel then head loss in both the pipe will be same then 4flv^2/2gd = constant now for the two pipe l, d are same and f1/f2=4 or f2/f1=1/4 then f1v1^2=f2v2^2 then v1/v2= root of f2/f1= root of 1/4 =1/2.

Now Q1/Q2=A1v1/A2v2 =v1/v2 = 1/2 = 0.5.

If two pipe in parallel then head loss in both the pipe will be same then 4flv^2/2gd = constant now for the two pipe l, d are same and f1/f2=4 or f2/f1=1/4 then f1v1^2=f2v2^2 then v1/v2= root of f2/f1= root of 1/4 =1/2.

Now Q1/Q2=A1v1/A2v2 =v1/v2 = 1/2 = 0.5.

Arul said:
7 years ago

D is the correct answer.

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