Tentafrågor

Question 1

1. Water at 20°C is flowing uniformly in a wide rectangular channel at an average
   velocity of 2 m/s. If the water depth is 0.2 m, the flow is:

a) subcritical
b) supercritical
c) critical
d) laminar

Answer 1

b) supercritical

Question 2

2. It is possible to determine the magnitude of the hydrostatic force acting on a plane
   surface submerged in water regardless of its shape and orientation, if one knows the
   vertical distance of the centroid of the surface from the free surface

a) TRUE
b) FALSE
c) Only if the surface is symmetrical
d) Only if one knows also the area of the surface

Answer 2

d) Only if one knows also the area of the surface

Question 3

3. Consider the flow of oil with density ρ= 894 kg/m 3 and μ = 2.33 kg/m · s in a 40-
   cm-diameter pipeline at an average velocity of 0.5 m/s. Neglecting local losses, the
   pressure drop ∆P along a 300-m length of the pipeline is:

a) 0,23 kPa
b) 101 kPa
c) 70 kPa
d) 7,9 kPa

Answer 3

c) 70 kPa

Question 4

4. The gage pressure in a liquid at a depth of 3 m is read to be 28 kPa.
   The density of the liquid is unknown.
   The gage pressure in the same liquid at a depth of 12 m is:
   a) 112 kPa
   b) 7 kPa
   c) 101 kPa
   d) Can’t be calculated if the density of the fluid is not known

Answer 4

a) 112 kPa

Question 5

1. A mercury manometer (ρ = 13,600 kg/m 3
   ) is connected to an air pipe to measure the
   pressure inside. The difference in the manometer levels is 15 mm, and the atmospheric
   pressure is 100 kPa. The absolute pressure in the duct air pipe is:

a) 98 kPa
b) 102 kPa
c) 2 kPa
d) 100 kPa

Answer 5

b) 102 kPa

Question 6

2. The figure shows a water pipe out of a reservoir. The distributed losses over 2000 m have
   been estimated as JL 12,24 m and the local losses as ∆hloc = 0,22 m.
   The water raise, h, in the piezometer inserted in the pipe at distance L = 200m from the
   reservoir is:

H= 30

a) About 42,46 m
b) About 17,54 m
c) About 10,29 m
d) About 30 m

Answer 6

b) About 17,54 m

Question 7

3. Consider steady flow in an open channel of rectangular cross section. If the river bed has
   a constant slope of 5°, the slope of the water free surface is also 5°:

a) Always true
b) Only if the flow is uniform
c) Only if the flow is non-uniform
d) Never

Answer 7

b) Only if the flow is uniform

Question 8

4. Consider fully developed laminar flow in a circular pipe. If the viscosity of the fluid is
   reduced by half by heating while the flow rate is held constant, the head loss:

a) reduces by half
b) is doubled
c) increases by a factor of 4
d) decreases by a factor of 4

Answer 8

a) reduces by half

Question 9

1. A tank of water is located in a city where the barometric reading is 760mm mercury. At a
   depth of 6m below the free surface of that tank, the absolute pressure, in Pascal, is:
   (density mercury 13570 kg/m 3
   , gravity: 9.81m/s2
   , density water: 1000 kg/m3
   )

a) 101172 Pa
b) 58860 Pa
c) 160032.5 Pa
d) 82.42 Pa
e) 42312.49 Pa

Answer 9

c) 160032.5 Pa

Question 10

The top infinite plate is moved to the right with a constant velocity, u = 10 m/s, under the
action of a force F= 3 N. The bottom plate is stationary.
The viscosity of the fluid is:

h = 1 mm
b = 50 mm
l = 100 mm

a) 0.06 Ns/m 2
b) 0.06 Nsm 2
c) 60 Ns/m 2
d) 60 Nsm 2

Answer 10

a) 0.06 N*s/m 2

Question 11

3. Consider uniform flow through an open channel with a Manning roughness coefficient of
   n = 0.015. If the Manning coefficient doubles (n = 0.030) as a result of some algae growth
   and the cross section remains constant, the discharge will:

a) double
b) decrease by a factor of 2 ,
c) remain unchanged,
d) decrease by half

Answer 11

d) decrease by half

Question 12

4. Water flows from reservoir A into pipe 1 (length L1, diameter D1, distributed losses J1),
   through a turbine and then through pipe 2 (length L1, diameter D1, distributed losses J1) is
   discharged into reservoir B. The most accurate expression to estimate the head ∆H at the
   turbine is:

Answer 12

Skriv ekvationen

Question 13

I.1 Consider steady flow in an open channel of rectangular cross section with a constant
river bed slope of 7°. Will the slope of the free surface also be 7°?

(a) Yes, in any flow condition
(b) Yes, in uniform flow
(c) Yes, in gradually varied flow
(d) No, never

Answer 13

(b) Yes, in uniform flow

Question 14

I.2 A vacuum gage connected to a tank reads 30 kPa at a location where the barometric
reading is 755 mmHg. How much is the absolute pressure in the tank? (Take density of
mercury: 13,590 kg/m 3
)

(a) 70,6 kPa
(b) 130,6 kPa
(c) 37,4 kPa
(d) 131 kPa

Answer 14

(a) 70,6 kPa

Question 15

II.3 Consider fully developed laminar flow in a circular pipe. If the velocity of the flow is
doubled while the diameter and the pipe length are held constant, the head loss will:

(a) increase by a factor of 2
(b) increase by a factor of 4
(c) decrease by a factor of 2
(d) decrease by a factor of 4

Answer 15

(a) increase by a factor of 2

Question 16

I.4 Consider three fluids: oil, water and air.
Which of the following 4 graphs represents the correct rate of deformation versus shear
stress behavior for these three fluids?

Question 17

II.1 Consider fully developed flow in a circular pipe with negligible local losses. If the
length of the pipe is doubled, the head loss ∆H will:

(a) double
(b) more than double
(c) less than double
(d) reduce by half
(e) remain constant

Answer 17

(a) double

Question 18

I.2 Consider fully developed laminar flow in a circular pipe. If the diameter of the pipe
is reduced by half while the flow rate and the pipe length are held constant, the head
loss will:

(a) double
(b) triple
(c) quadruple
(d) increase by a factor of 8
(e) increase by a factor of 16

Answer 18

(e) increase by a factor of 16

Question 19

II.3 The tank in the figure contains water for a depth of 10m, as shown (width is 5 m
and walls are vertical).
What is the depth in meters of the center of pressure yCP , of the resultant force, R,
due to the liquid?
a) 5.0
b) 6.67
c) 3.33
d) 2.0
e) 10.0

Answer 19

b) 6.67

Question 20

II.4 What is the magnitude of the resultant force, R, in the previous question in
Newtons per meter (N/m)?

h= 10 m
w = 5 m

a) 245 000
b) 981 000
c) 98 100
d) 49 050
e) 490 500

Answer 20

e) 490 500

Question 21

II.2. The Froud number in a given cross section of a river can be used to assess whether the
flow is:

a) laminar
b) critical
c) uniform
d) goes through hydraulic jump

Answer 21

b) critical

Question 22

II.1. The air pressure in an air duct is measured by a mercury manometer attached to it The
mercury-level difference between the two columns is 15 mm. The absolute pressure in the
duct is:

Density of mercury ; 13600 kg/m

a) 103001,2 kPa
b) 101000 Pa
c) 98998,76 kPa
d) 0 kPa

Answer 22

a) 103001,2 kPa

Question 23

I.1 Water is flowing uniformly in a 4-m-wide rectangular channel at an average
velocity of 8 m/s. If the water depth is 20 cm, determine whether the flow is:

(a) subcritical
(b) critical
(c) supercritical
(d) can’t be determined

Answer 23

(c) supercritical

Question 24

I.1 Water is flowing uniformly in a 4-m-wide rectangular channel at an average
velocity of 8 m/s. If the water depth is 20 cm, determine whether the flow is:

(a) subcritical
(b) critical
(c) supercritical
(d) can’t be determined

Answer 24

(c) supercritical

Question 25

I.2 Liquid ammonia at 20°C is flowing through a 5-mm-diameter copper pipe at a rate
of 0.15 kg/s. Density and viscosity of the ammonia are: ρ = 665.1 kg/m 3 and μ =
2.361×10-4 kg/ms.
The flow is:

(a) laminar
(b) turbulent
(c) transitional
(d) can’t be determined with given data

Answer 25

(b) turbulent

Question 26

II.3 The tank in the figure below contains water for a depth of 5m, as shown (the
width of the tank is 2 m and walls are vertical).
What is the magnitude of the resultant force, R, in N/m, applied to the vertical wall?
(ρ=100 kg/m 3 ; g=9,8 m/s2 )

(a)122500
(b)245000
c) 163333
(d) 490000
(e) 490500

Answer 26

(a)122500

Question 27

What depth of oil (in m) with relative density 0.75, will give a gauge pressure of
275000 Pa? (g=9,8 m/s2)
(a) 37.38
(b) 367
(c) 0.027
d) 20.2 × 104
(e) 28.03

Answer 27

(a) 37.38

Question 28

II.1 Water is flowing downstream of a dam spillway at a velocity V = 8 m/s in a rectangular
channel. The water depth is h1 = 0,5 m. A hydraulic jump is expected to happen.
The conjugate depth at the hydraulic jump h2 is:

a) about 3,6 m
b) about 2,3 m
c) there will not be hydraulic jump
d) h1 is equal to h2

Answer 28

b) about 2,3 m

Question 29

II.2 The funnel in the figure is filled with oil (ρoil = 880 kg/m3 ; layer AB = 0,3 m) and water
(ρwater = 1000 kg/m3 ; layer BC = 0,4 m). The tube on the side contains mercury from C to D
(ρmercury = 13550 kg/m3
).

The height h is:
a) about 0,65 m
b) about 0,75 m
c) about 0,3 m
d) about 0,4

Answer 29

a) about 0,65 m

Question 30

II.3 The figure below shows a small hydropower plant. Knowing that the geodetic head is 60
m, the velocity of the water in the pipe is V = 24 m/s and total head losses are 4 m, the head
at the turbine that can be used for producing power is:

a) 26,6 m
b) 93,4 m
c) 60 m
d) 56 m

Answer 30

a) 26,6 m

Question 31

2. Consider the figure below: a horizontal jet of blue fluid exits from a nozzle of constant cross section and strikes a vertical plate. A resultant force FR is needed to hold the plate in place so that it does not move when the jet strikes it.
   If the velocity at which the blue jet strikes the plate is doubled, the resultant force FR will:

a) double
b) be reduced by half
c) will increase by a factor of 4
d) will be decreased by a factor of 4

Answer 31

c) will increase by a factor of 4

Question 32

4. Oil flows at a velocity of V = 0,8 m/s in a horizontal pipe for 3 km. The pipe has a dimeter of 250 mm and the kinematic viscosity of the oil, ν is 0,12*10-3 m2/s. The head losses in the pipe are:

a) about 15 m
b) zero
c) it depends on the roughness of the pipe d) about 0,038 m