Question

Venturi meter

Answer 1

Can you answer some simple questions to work this problem out?

Answer 2

Yes. I did. i just dont understand the problem.. especially the area of the subject is 4 times bla bla. can you help me?

Answer 3

Yes, I can. Tell me what you mean by the rate of flow of water

Answer 4

volume of liquid passing through the constricted section.

Answer 5

my answer of the area of the pipe was 100cm^2.. and im not sure

Answer 6

Right! volume of liquid passing through the Venturi tube ( any cross section ) per unit time.

Answer 7

Area of the pipe is 4 times 20 cm^2 = 80 cm^2

Answer 8

ah yes! its 80. typo.

Answer 9

so is this the area of the larger pipe?

Answer 10

Yes

Answer 11

Actually, you don't need area of larger pipe! Do you know the formula for flow rate ?

Answer 12

ah yes its r= area * volume..

Answer 13

Nope!
r = area*velocity of water = A*v

Answer 14

Ah yes. im so sorry.

Answer 15

OK, so you have area of constricted pipe = 20 cm^2. What is the velocity of water in that region ?

Answer 16

I used a1/a2 = v2/v1

Answer 17

Good! then ?

Answer 18

I, first solve the a1/a2.. its 80/20.. am i in the right process?

Answer 19

Right, you are absolutely right!

Answer 20

then i solve the velocity of the pipe since the diff of the two pipes is given

Answer 21

Difference of pressure is given. Right. Then ?

Answer 22

its like this. 6.5 = 1/2 (1 g/cm^3) ( [ 16-1]) V

Answer 23

velocity would be 0.93

Answer 24

unit of velocity ?

Answer 25

Unit inconsistency is there!

Answer 26

cm/s. hehe sorry

Answer 27

velocity's right?

Answer 28

Nope! Unit and the value of velocity both are wrong..

Answer 29

Pressure is 6.5 N /cm^2 and density of water you are using in g/cm^3! That is the catch.

Answer 30

Ah. My bad. Okay wait. I'll solve it again

Answer 31

OK

Answer 32

velocity's 9.31?

Answer 33

unit ?

Answer 34

cm/s

Answer 35

Ok, what is rate now ?

Answer 36

should i get the velocity of the water in the constriction?

Answer 37

This is the velocity in large cross section. Right? Then use area of large cross section.
If you want to use area of constricted pipe, you have to calculate velocity in that region. Both will give same answer.

Answer 38

You get the correct answer ?

Answer 39

i tried the constricted area and i got.. its so far from the real answer

Answer 40

Oops...! Actually, it should be 6.5 = 1/2 (1 g/cm^3) ( [ 16-1]) V^2

Answer 41

Now do the same calculations again. This time you'll get correct result. :)

Answer 42

v2 is 0.93 cm/s

Answer 43

0.93 is v^2 ! Take square root of 0.93 to get velocity in the larger cross section

Answer 44

what area should i use to get the rate?

Answer 45

wait. thats the answer. its 0.93. i took the square root.

Answer 46

Sorry! It's not 0.93, it's 9.3. Take square root of it and then multiply it by the area of large cross section

Answer 47

\[Rate \ = Area * Velocity = 80 * \sqrt{9.3} \ cm^3/ s\]

Answer 48

its 243..

Answer 49

how come.. the answer key gave me 232

Answer 50

Wait... Check your velocity. It's wrong. It should be v^2 = 8.666. Use it. I am getting correct result.

Answer 51

v = 2.944 cm/s

Answer 52

6.5 = 1/2 (1 g/cm^3) ( [ 16-1]) V^2

Answer 53

ah yes youre right

Answer 54

Right! in place of 1 g/cm^3 use 0.001 kg/cm^3

Answer 55

Finally. its almost there. its 236