Bank Question FE - Pressure measurement

Fluid Mechanics
Pressure
Measurement

Contents

CC303 Jun 2014................................2
CC303 Dec 2013 ...............................3
CC303 Jun 2012................................5
CC5143 Jun 2017..............................6
CC5143 Jun 2018..............................7
CC5143 Dis 2018 ..............................8
CC5143 Jun 2019..............................9
CC5143 Dis 2016 ............................ 10
CC5143 Dis 2017 ............................ 11
CC5143 Jun 2016............................ 13

DECEMBER 47

JKA, POLITEKNIK PORT DICKSON

1

CC303 Jun 2014

Q1) Calculate the water pressure in the depth of 4 m below the surface of water
(4 marks)

Answer:
Pressure, P = gh
= 1000 x 9.81 x 4 = 39240 N/m2

Q2) Calculate the height of oil piezometer with specific gravity of 0.83 cause by a pressure of
2500 N/m2.

(4 marks)
Answer:

Pressure, P = gh
2500 = ( 0.83 X 100 ) x 9.81 x h
h = 0.307 m
Q3) An inverted differential manometer is shown in Figure 1. Determine the differences of
pressure between the two pipes if the specific gravity of oil X = 0.8, oil Y = 0.9 and mercury =
13.6. The given values of h1-= 60 cm, h2 = 55 cm and Q is ¼ from the height of h1.

Figure 1
(14 marks)

Answer:
PM - 1 g h1 - 2 g h2 - 3 g h3 = PN - 4 g h4
PM - water g h1 - oil x g h2 - mercury g h3 = PN -  oil y g h4
PM –[1000 x 9.81 x (1/4 x 0.6)] - [(0.8 x 1000) x 9.81 x (0.6 - 0.15)] - [(13.6 x 1000) x 9.81 x
((0.55+ 0.15) – 0.6))] = PN – [(0.9 x 1000) x 9.81 x 0.55]

PM –[1000 x 9.81 x 015] - [(0.8 x 1000) x 9.81 x 0.45)] - [(13.6 x 1000) x 9.81 x 0.1] = PN – [(0.9 x 1000) x 9.81 x 0.55]

PM – PN = 1471.5 + 3531.6 + 13341.6 – 4855.95 = 13488.75 N/m3

2

CC303 Dec 2013

Q1) Determine the pressure at the depth of 500 cm from the surface of liquid which has a
relative density of 0.8

(4 marks)
Answer :

Pressure, P = gh
= 1000 x 9.81 x 4 = 39240 N/m2

Q2) Determine the height of water in a tube pressure at base is 200 N/m2.
(4 marks)

Answer :
Pressure, P = gh
200 = 1000 x 9.81 x h
h = 0.020 m = 20cm

Q3) Describe pressure and pressure head with formula
(4 marks)

Answer :
Pressure P = F/A
Pressure head, P = gh

Q4) If the level of oil on left limb is 9 cm below pipe P and the mercury on the right limb is 5 cm
above pipe P, calculate the pressure at P. (Specific gravity of oil = 0.80 & Patm = 1kPa)

Figure 2 (4 marks)

Answer :
Pleft = Pright
P + oil g h1 = Patm + mercury g h2
P + {(0.8 x 1000) 9.81 x 0.09} = 1000 + { (13.6 x 1000) 9.81 x (0.09 + 0.05) }
P = 18971.92 N/m2

3

Q5) Calculate the head of an oil column with a specific gravity of 0.8 that is equivalent to a gauge
pressure of 30 kN/m2.

(4 marks)
Answer:

Pressure, P = gh
30 000 = (0.8 x 1000) x 9.81 x h
h = 3.823 m
Q6) By referring Figure 2, calculate the difference of pressure between pipe A and pipe B.

Figure 3
(16 marks)

Answer:
Pleft = Pright
PA + oil g h1 = PB + mercury g h2 + oil g h3
PA + { (0.8 x 1000) 9.81 x (0.2+0.15+0.3)} = PB + { (13.6 x 1000) 9.81 x (0.2) } + { (0.8 x 1000) 9.81
x (0.15) }
PA + { (0.8 x 1000) 9.81 x (0.65)} = PB + { (13.6 x 1000) 9.81 x (0.2) } + { (0.8 x 1000) 9.81 x (0.15) }
PA - PB = 22759.2 N/m2 @ 22.759 kN/m2

4

CC303 Jun 2012 (4 marks)

Q1) State FOUR (4) types of manometers

Answer :
1) Simple manometer
2) Micro-manometer
3) Differential manometer
4) Inverted Differential manometer

Q2) Define gauge pressure and absolute pressure
(4 marks)

Answer :
Gauge pressure measured with the help of a pressure measuring instrument, in which
the atmospheric pressure id taken as datum
It is the pressure equal to the algebraic sum of atmosphere and gauge pressures.

5

CC5143 Jun 2017

Q1) Calculate the absolute water pressure at the depth 4 m below the surface of water. Take
atmosphere pressure 101.3 kN/m2.

(6 marks)
Answer :

Pgauge = gh
= 1000 x 9.81 x4 = 39240 N/m2 @ Pa

Pabsolute = Pgauge + Patm
= 39240 + (101.3 x 1000) = 140540 N/m2 @ Pa

Q2) Figure 4 shows differential manometer. The liquid of M and N is oil (sg= 0.8) and the
specific gravity of mercury is 13.6, calculate the difference pressure between pipe M and N if
the h1 = 100 cm, h2 = 60 cm and h3 = 20 cm.

Figure 4

(14 marks)
Answer :
Pleft = Pright
PM + oil g h1 = PN + mercury g h2 + oil g h3
PA + {(0.8 x 1000) 9.81 x 1} = PB + {(13.6 x 1000) x 9.81 x (0.2)} + {(0.8 x 1000) 9.81 x (0.6 - 0.2)}
PA + {(0.8 x 1000) 9.81 x 1} = PB + {(13.6 x 1000) x 9.81 x (0.2)} + {(0.8 x 1000) 9.81 x (0.4)}
PA + 7848 = PB + 26683.2 + 3139.2
PA - PB = 21974.4 N/m2 @ 21.974 kN/m2

6

CC5143 Jun 2018

Figure 5 shows a differential manometer. Pipe A and pipe B contains oil of specific gravity 0.95.
If the pressure at pipe A and Pipe B are 222.5 kN/m2 and 165.0 kN/m2, calculate the value of h.

Figure 5 (14 marks)

Answer :
Pleft = Pright
PA + 1 g h1 = PB + mercury g h2 + 2 g h3

222.5x103 + {(0.95 x 1000) x 9.81 x (0.5 +h)} = 165x103 + {(13.6 x 1000) x 9.81 x h} + {(0.95 x 1000) x 9.81 x
(1.8+0.5)}

222.5x103 + {(4659.75 + 9319.5h} = 165x103 + {133416 h} + {21434.85}
227159.75 + 9319.5h = 133416 h + 186434.85
-124096.5 h = -40724.9
h = 0.328m

7

CC5143 Dis 2018

The left limb of u-tube mercury manometer shown in Figure 6 is connected to a pipeline
conveying water. The level of mercury in left limb being 56cm below the center of the pipeline
and right limb being open to atmosphere. The level of mercury in the right limb is 46cm above
that of the left limb containing a liquid of specific gravity 0.88 to a height 36 cm. Calculate the
gauge pressure in the pipe.

Figure 6
(14 marks)

Answer :
Pleft = Pright
PA + 1 g h1 = 2 g h2 + 3 g h3 + Patm
PA + {1000 x 9.81 x 0.56} = {(13.6 x 1000) x 9.81 x 0.46} + {(0.88 x 1000) x 9.81 x 0.36}
PA + 5493.6 = 61371.36 + 3107.808
PA = 58985.568 N/m2 = 58.986 kN/m2

8

CC5143 Jun 2019

U-tube differential manometer shown in Figure 7 connects pipe A and B. Pipe A contains a liquid
of specific gravity 1.594 under a pressure of 10.3 x 104 N/m2 and pipe B contains oil of specific
gravity 0.8 under a pressure 17.16 x 104 N/m2. Pipe A lies 2.5 m above pipe B, Calculate the
value of h.

Figure 7

(12 marks)

Answer :
Pleft = Pright
PA + 1 g h1 + 2 g h2 = 3 g h3 + PB

10.3 x 104 + {(1.594x1000) x 9.81 x (2.5+1.5)} + {(13.6 x 1000) x 9.81 x h} = {(0.8 x 1000) x 9.81 x (1.5 +
h)} + 17.16 x 104

10.3 x 104 + 62548.56 + 133416 h = 11772 + 7848 h + + 17.16 x 104
10.3 x 104 + 39240 + 133416 h = 11772 + 7848 h + + 17.16 x 104
125568 h = 17823.44
h = 0.142 m

9

CC5143 Dis 2016

Referring to Figure 8, fluid A is water and fluid B is gasoline with specific gravity of 0.739. The
pressure at point B is 175 kN/m2. Calculate the water pressure of the system

Figure 8
(14 marks)

Answer :
Pleft = Pright
PA + 1 g h1 = 2 g h2 + 3 g h3 + PB
PA + {1000 x 9.81 x 0.7} = {(13.6 x 1000) x 9.81 x 0.4} + {(0.739 x 1000) x 9.81 x 0.6} +
175 x103
PA + 6867 = 53366.4 + 4349.754 + 175 x103
PA = 225849.154 N/m2 @ 225.85 kN/m2

10

CC5143 Dis 2017

Q1) Figure 9 below shows a piezometer tube attached to the pipe contains oil with a specific
gravity = 0.95. If the level of the oil in the tube rises to 150 mm, calculate the pressure, P in the
pipe

Figure 9 (6 marks)

Answer :
Pressure, P = gh
= (0.95 x 1000) x 9.81 x 0.15 = 1897.93 N/m2

Q2) A U-tube differential manometer is connected to pipe M and pipe N as shown in Figure 10.

Pipe M flows water with the density ρw = 1000 kg/m3 and in pipe N contains oil with the density
ρo = 900 kg/m3. If the pressure in pipe M is 100kN/m2, and U-tube contains mercury (ρw =
13600 kg/m3), calculate the pressure in pipe N.

Figure 10

11

(6 marks)
Answer:

Pleft = Pright
PM + 1 g h1 = 2 g h2 + 3 g h3 + PN
100 x 103 + {1000 x 9.81 x 1} = {(13.6 x 1000) x 9.81 x 1.5 } + {900 x 9.81 x 0.5} + PN
109810 = 200124 + 4414.5 + PN
PN = 94728.5 N/m2 @ 94.728 kN/m2

12

CC5143 Jun 2016

Q1) An object is located at a depth of 2 m from the surface of an oil with specific weight of 8.0
kN/m3. Calculate:
i. Intensity of pressure at the point.
ii. The height of water column corresponding to the value of pressure

(6 marks)

Answer:
Pressure, P = gh

= (0.95 x 1000) x 9.81 x 0.15 = 1897.93 N/m2

Q2) A differential manometer is connected to pipe A and B containing oil with specific gravity
0.8. The difference in mercury levels is 100 mm. Based on Figure 11, determine the pressure
difference between the two pipes.

Figure 11
(6 marks)

Answer:
Pleft = Pright
PA + 1 g h1 + 2 g h2 = 3 g h3 + PB

PA + {(0.8 x 1000) x 9.81 x (0.1 + 0.05 + 0.06)} + {(13.6 x 1000) x 9.81 x 0.1} = {(0.8 x 1000) x 9.81 x (0.1 + 0.05)} +
PB

13

PA + 1648.08 + 13341.6 = 1177.2 + PB
PA – PB = -13812.48 N/m2 @ - 13.812 kN/m2
PB – PA = 13812.48 N/m2 @ 13.812 kN/m2

14