Fluid Mechanics Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The force required to separate two glass plates of area
10
–2
m
–2
 with a film of water 0.05 m thick between them, is
(Surface tension of water is 70 × 10
–3
 N/m)
(a) 28 
N
(b) 14 
N
(c) 50 
N
(d) 38 
N
Q.2 A thin metal disc of radius 
r
floats on water surface and bends
the surface downwards along the perimeter making an angle q
with vertical edge of the disc. If the disc displaces a weight of
water 
W
and surface tension of water is T, then the weight of
metal disc is
(a)
2p+ rTW
(b)
2 cos p q- rTW
(c)
2 cos p q+ rTW
(d)
2 cos -pq W rT
Q.3 The amount of work done in blowing a soap bubble such that its
diameter increases from d to D is (T = surface tension of the
solution)
(a)
22
4() p- D dT (b)
22
8() p- D dT
(c)
22
() p- D dT (d)
22
2() p- D dT
Q.4 A film of water is formed between two straight parallel
wires of length 10 cm each separated by 0.5 cm. If their
separation is increased by 1 mm while still maintaining their
parallelism, how much work will have to be done (Surface
tension of water = 70 × 10
–2
 N/m)
(a) 7.22 × 10
–6 
Joule (b) 1.44 × 10
–5 
Joule
(c) 2.88 × 10
–5
 Joule (d) 5.76 × 10
–5 
Joule
Page 2


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The force required to separate two glass plates of area
10
–2
m
–2
 with a film of water 0.05 m thick between them, is
(Surface tension of water is 70 × 10
–3
 N/m)
(a) 28 
N
(b) 14 
N
(c) 50 
N
(d) 38 
N
Q.2 A thin metal disc of radius 
r
floats on water surface and bends
the surface downwards along the perimeter making an angle q
with vertical edge of the disc. If the disc displaces a weight of
water 
W
and surface tension of water is T, then the weight of
metal disc is
(a)
2p+ rTW
(b)
2 cos p q- rTW
(c)
2 cos p q+ rTW
(d)
2 cos -pq W rT
Q.3 The amount of work done in blowing a soap bubble such that its
diameter increases from d to D is (T = surface tension of the
solution)
(a)
22
4() p- D dT (b)
22
8() p- D dT
(c)
22
() p- D dT (d)
22
2() p- D dT
Q.4 A film of water is formed between two straight parallel
wires of length 10 cm each separated by 0.5 cm. If their
separation is increased by 1 mm while still maintaining their
parallelism, how much work will have to be done (Surface
tension of water = 70 × 10
–2
 N/m)
(a) 7.22 × 10
–6 
Joule (b) 1.44 × 10
–5 
Joule
(c) 2.88 × 10
–5
 Joule (d) 5.76 × 10
–5 
Joule
2
DPP/ P 21
Q.5 The liquid meniscus in capillary tube will be convex, if the
angle of contact is
(a) Greater than 90° (b) Less than 90°
(c) Equal to 90° (d) Equal to 0°
Q.6 Two soap bubbles of radii r
1
 and r
2
 equal to 4 cm  and 5 cm
are touching each other over a common surface S
1
S
2
(shown in figure). Its radius will be
(a) 4 cm
(b) 20 cm
5 cm 4 cm
S
1
S
2
(c) 5 cm
(d) 4.5 cm
Q.7 The radii of two soap bubbles are 
1
r and 
2
r . In isothermal
conditions, two meet together in vaccum. Then the radius
R of the resultant bubble is given by
(a)
12
( )/2 =+ R rr (b)
1122
() R rrrr =+
(c)
2 22
12
R rr =+
(d)
12
R rr =+
Q.8 Two parallel glass plates are dipped partly in the liquid of
density '' d keeping them vertical. If the distance between
the plates is 
'' x
, surface tension for liquids is T and angle
of contact is 
q
, then rise of liquid between the plates due
to capillary will be
(a)
cos q T
xd
(b)
2 cos q T
xdg
(c)
2
cos q
T
xdg
(d) 
cos q T
xdg
Q.9 A capillary tube of radius R is immersed in water and water
rises in it to a height H . Mass of water in the capillary
tube is . M If the radius of the tube is doubled, mass of
water that will rise in the capillary tube will now be
(a)
M
(b)
2M
(c)
/2 M
(d)
4M
Q.10 In a surface tension experiment with a capillary tube water
rises upto 0.1 m. If the same experiment is repeated on an
artificial satellite, which is revolving around the earth, water
will rise in the capillary tube upto a heights of
(a) 0.1 m
(b) 0.2 m
(c) 0.98 m
(d) Full length of the capillary tube
Q.11 Which graph represents the variation of surface tension
with temperature over small temperature ranges for water ?
(a)
S.T.
T emp.
(b)
S.T.
T emp.
(c)
S.T.
T emp.
(d)
S.T.
T emp.
Q.12 A solid sphere of density h (
1 >
) times lighter than water
is suspended in a water tank by a string tied to its base as
shown in fig. If the mass of the sphere is m then the tension
in the string is given by
(a)
1 æö h-
ç÷
èø h
mg
 (b) hmg
(c)
1 h-
mg
  (d) ( 1) h- mg
Q.13 A candle of diameter d is floating on a liquid in a cylindrical
container of diameter D() Dd >> as shown in figure. If it
is burning at the rate of 2 cm/ hour then the top of the candle
will
D
d
L
L
(a) Remain at the same height
(b) Fall at the rate of 1 cm/hour                
(c) Fall at the rate of 2 cm/hour
(d) Go up the rate of 1 cm/hour
Page 3


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The force required to separate two glass plates of area
10
–2
m
–2
 with a film of water 0.05 m thick between them, is
(Surface tension of water is 70 × 10
–3
 N/m)
(a) 28 
N
(b) 14 
N
(c) 50 
N
(d) 38 
N
Q.2 A thin metal disc of radius 
r
floats on water surface and bends
the surface downwards along the perimeter making an angle q
with vertical edge of the disc. If the disc displaces a weight of
water 
W
and surface tension of water is T, then the weight of
metal disc is
(a)
2p+ rTW
(b)
2 cos p q- rTW
(c)
2 cos p q+ rTW
(d)
2 cos -pq W rT
Q.3 The amount of work done in blowing a soap bubble such that its
diameter increases from d to D is (T = surface tension of the
solution)
(a)
22
4() p- D dT (b)
22
8() p- D dT
(c)
22
() p- D dT (d)
22
2() p- D dT
Q.4 A film of water is formed between two straight parallel
wires of length 10 cm each separated by 0.5 cm. If their
separation is increased by 1 mm while still maintaining their
parallelism, how much work will have to be done (Surface
tension of water = 70 × 10
–2
 N/m)
(a) 7.22 × 10
–6 
Joule (b) 1.44 × 10
–5 
Joule
(c) 2.88 × 10
–5
 Joule (d) 5.76 × 10
–5 
Joule
2
DPP/ P 21
Q.5 The liquid meniscus in capillary tube will be convex, if the
angle of contact is
(a) Greater than 90° (b) Less than 90°
(c) Equal to 90° (d) Equal to 0°
Q.6 Two soap bubbles of radii r
1
 and r
2
 equal to 4 cm  and 5 cm
are touching each other over a common surface S
1
S
2
(shown in figure). Its radius will be
(a) 4 cm
(b) 20 cm
5 cm 4 cm
S
1
S
2
(c) 5 cm
(d) 4.5 cm
Q.7 The radii of two soap bubbles are 
1
r and 
2
r . In isothermal
conditions, two meet together in vaccum. Then the radius
R of the resultant bubble is given by
(a)
12
( )/2 =+ R rr (b)
1122
() R rrrr =+
(c)
2 22
12
R rr =+
(d)
12
R rr =+
Q.8 Two parallel glass plates are dipped partly in the liquid of
density '' d keeping them vertical. If the distance between
the plates is 
'' x
, surface tension for liquids is T and angle
of contact is 
q
, then rise of liquid between the plates due
to capillary will be
(a)
cos q T
xd
(b)
2 cos q T
xdg
(c)
2
cos q
T
xdg
(d) 
cos q T
xdg
Q.9 A capillary tube of radius R is immersed in water and water
rises in it to a height H . Mass of water in the capillary
tube is . M If the radius of the tube is doubled, mass of
water that will rise in the capillary tube will now be
(a)
M
(b)
2M
(c)
/2 M
(d)
4M
Q.10 In a surface tension experiment with a capillary tube water
rises upto 0.1 m. If the same experiment is repeated on an
artificial satellite, which is revolving around the earth, water
will rise in the capillary tube upto a heights of
(a) 0.1 m
(b) 0.2 m
(c) 0.98 m
(d) Full length of the capillary tube
Q.11 Which graph represents the variation of surface tension
with temperature over small temperature ranges for water ?
(a)
S.T.
T emp.
(b)
S.T.
T emp.
(c)
S.T.
T emp.
(d)
S.T.
T emp.
Q.12 A solid sphere of density h (
1 >
) times lighter than water
is suspended in a water tank by a string tied to its base as
shown in fig. If the mass of the sphere is m then the tension
in the string is given by
(a)
1 æö h-
ç÷
èø h
mg
 (b) hmg
(c)
1 h-
mg
  (d) ( 1) h- mg
Q.13 A candle of diameter d is floating on a liquid in a cylindrical
container of diameter D() Dd >> as shown in figure. If it
is burning at the rate of 2 cm/ hour then the top of the candle
will
D
d
L
L
(a) Remain at the same height
(b) Fall at the rate of 1 cm/hour                
(c) Fall at the rate of 2 cm/hour
(d) Go up the rate of 1 cm/hour
DPP/ P 21
3
Q.14 A viscous fluid is flowing through a cylindrical tube. The
velocity distribution of the fluid is best represented by the
diagram
  (a) (b) 
(c) (d) None of these
Q.15 When a body falls in air, the resistance of air depends to a
great extent on the shape of the body, 3 different shapes
are given. Identify the combination of air resistances which
truly represents the physical situation. (The cross sectional
areas are the same).
R R R
W W W
(1)
Disc
(2)
Ball
(3)
Cigar shaped
(a)
1 23 <<
(b)
2 31 <<
(c)
3 21 <<
(d)
3 12 <<
Q.16A homogeneous solid cylinder of length ( /2) < LLH .
Cross-sectional area A/5 is immersed such that it floats
with its axis vertical at the liquid-liquid interface with length
L/4 in the denser liquid as shown in the fig. The lower
density liquid is open to atmosphere having pressure P
0
.
Then density of solid is given by
H/2
H/2
3 /4 L
2d
d
(a)
5
4
d (b)
4
5
d
(c)
d
(d)
5
d
Q.17 A large open tank has two holes in the wall. One is a square
hole of side L at a depth y from the top and the other is a
circular hole of radius R at a depth 4y from the top. When
the tank is completely filled with water the quantities of
water flowing out per second from both the holes are the
same. Then R is equal to
(a)
2 L p
(b)
2
L
p
(c) L (d)
2
L
p
Q.18 Water is filled in a cylindrical container to a height of 3m.
The ratio of the cross-sectional area of the orifice and the
beaker is 0.1. The square of the speed of the liquid coming
out from the orifice is (g = 10m/s
2
)
(a)
22
50 m /s
(b)
22
50.5m /s
52.5 cm
3 m
(c)
22
51m /s
(d)
22
52 m /s
Q.19 An incompressible liquid flows through a horizontal tube
as shown in the following fig. Then the velocity v of the
fluid is
A
A
1.5A
v
1 
= 3 m/s
v
v
2 
= 1.5 m/s
(a) 3.0 m/s (b) 1.5 m/s (c) 1.0 m/s (d) 2.25 m/s
Q.20 Radius of a capillary tube is 2 × 10
–3
m. A liquid of weight
6.28 × 10
–4 
N may remain in the capillary tube then the
surface tension of liquid will be
(a) 5 × 10
–3
 N/m (b) 5 × 10
–2
 N/m
(c) 5 N/m (d) 50 N/m
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a)  1, 2 and 3 are correct (b)  1 and 2 are correct
(c)  2 and 4 are correct (d)  1 and 3 are correct
Page 4


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The force required to separate two glass plates of area
10
–2
m
–2
 with a film of water 0.05 m thick between them, is
(Surface tension of water is 70 × 10
–3
 N/m)
(a) 28 
N
(b) 14 
N
(c) 50 
N
(d) 38 
N
Q.2 A thin metal disc of radius 
r
floats on water surface and bends
the surface downwards along the perimeter making an angle q
with vertical edge of the disc. If the disc displaces a weight of
water 
W
and surface tension of water is T, then the weight of
metal disc is
(a)
2p+ rTW
(b)
2 cos p q- rTW
(c)
2 cos p q+ rTW
(d)
2 cos -pq W rT
Q.3 The amount of work done in blowing a soap bubble such that its
diameter increases from d to D is (T = surface tension of the
solution)
(a)
22
4() p- D dT (b)
22
8() p- D dT
(c)
22
() p- D dT (d)
22
2() p- D dT
Q.4 A film of water is formed between two straight parallel
wires of length 10 cm each separated by 0.5 cm. If their
separation is increased by 1 mm while still maintaining their
parallelism, how much work will have to be done (Surface
tension of water = 70 × 10
–2
 N/m)
(a) 7.22 × 10
–6 
Joule (b) 1.44 × 10
–5 
Joule
(c) 2.88 × 10
–5
 Joule (d) 5.76 × 10
–5 
Joule
2
DPP/ P 21
Q.5 The liquid meniscus in capillary tube will be convex, if the
angle of contact is
(a) Greater than 90° (b) Less than 90°
(c) Equal to 90° (d) Equal to 0°
Q.6 Two soap bubbles of radii r
1
 and r
2
 equal to 4 cm  and 5 cm
are touching each other over a common surface S
1
S
2
(shown in figure). Its radius will be
(a) 4 cm
(b) 20 cm
5 cm 4 cm
S
1
S
2
(c) 5 cm
(d) 4.5 cm
Q.7 The radii of two soap bubbles are 
1
r and 
2
r . In isothermal
conditions, two meet together in vaccum. Then the radius
R of the resultant bubble is given by
(a)
12
( )/2 =+ R rr (b)
1122
() R rrrr =+
(c)
2 22
12
R rr =+
(d)
12
R rr =+
Q.8 Two parallel glass plates are dipped partly in the liquid of
density '' d keeping them vertical. If the distance between
the plates is 
'' x
, surface tension for liquids is T and angle
of contact is 
q
, then rise of liquid between the plates due
to capillary will be
(a)
cos q T
xd
(b)
2 cos q T
xdg
(c)
2
cos q
T
xdg
(d) 
cos q T
xdg
Q.9 A capillary tube of radius R is immersed in water and water
rises in it to a height H . Mass of water in the capillary
tube is . M If the radius of the tube is doubled, mass of
water that will rise in the capillary tube will now be
(a)
M
(b)
2M
(c)
/2 M
(d)
4M
Q.10 In a surface tension experiment with a capillary tube water
rises upto 0.1 m. If the same experiment is repeated on an
artificial satellite, which is revolving around the earth, water
will rise in the capillary tube upto a heights of
(a) 0.1 m
(b) 0.2 m
(c) 0.98 m
(d) Full length of the capillary tube
Q.11 Which graph represents the variation of surface tension
with temperature over small temperature ranges for water ?
(a)
S.T.
T emp.
(b)
S.T.
T emp.
(c)
S.T.
T emp.
(d)
S.T.
T emp.
Q.12 A solid sphere of density h (
1 >
) times lighter than water
is suspended in a water tank by a string tied to its base as
shown in fig. If the mass of the sphere is m then the tension
in the string is given by
(a)
1 æö h-
ç÷
èø h
mg
 (b) hmg
(c)
1 h-
mg
  (d) ( 1) h- mg
Q.13 A candle of diameter d is floating on a liquid in a cylindrical
container of diameter D() Dd >> as shown in figure. If it
is burning at the rate of 2 cm/ hour then the top of the candle
will
D
d
L
L
(a) Remain at the same height
(b) Fall at the rate of 1 cm/hour                
(c) Fall at the rate of 2 cm/hour
(d) Go up the rate of 1 cm/hour
DPP/ P 21
3
Q.14 A viscous fluid is flowing through a cylindrical tube. The
velocity distribution of the fluid is best represented by the
diagram
  (a) (b) 
(c) (d) None of these
Q.15 When a body falls in air, the resistance of air depends to a
great extent on the shape of the body, 3 different shapes
are given. Identify the combination of air resistances which
truly represents the physical situation. (The cross sectional
areas are the same).
R R R
W W W
(1)
Disc
(2)
Ball
(3)
Cigar shaped
(a)
1 23 <<
(b)
2 31 <<
(c)
3 21 <<
(d)
3 12 <<
Q.16A homogeneous solid cylinder of length ( /2) < LLH .
Cross-sectional area A/5 is immersed such that it floats
with its axis vertical at the liquid-liquid interface with length
L/4 in the denser liquid as shown in the fig. The lower
density liquid is open to atmosphere having pressure P
0
.
Then density of solid is given by
H/2
H/2
3 /4 L
2d
d
(a)
5
4
d (b)
4
5
d
(c)
d
(d)
5
d
Q.17 A large open tank has two holes in the wall. One is a square
hole of side L at a depth y from the top and the other is a
circular hole of radius R at a depth 4y from the top. When
the tank is completely filled with water the quantities of
water flowing out per second from both the holes are the
same. Then R is equal to
(a)
2 L p
(b)
2
L
p
(c) L (d)
2
L
p
Q.18 Water is filled in a cylindrical container to a height of 3m.
The ratio of the cross-sectional area of the orifice and the
beaker is 0.1. The square of the speed of the liquid coming
out from the orifice is (g = 10m/s
2
)
(a)
22
50 m /s
(b)
22
50.5m /s
52.5 cm
3 m
(c)
22
51m /s
(d)
22
52 m /s
Q.19 An incompressible liquid flows through a horizontal tube
as shown in the following fig. Then the velocity v of the
fluid is
A
A
1.5A
v
1 
= 3 m/s
v
v
2 
= 1.5 m/s
(a) 3.0 m/s (b) 1.5 m/s (c) 1.0 m/s (d) 2.25 m/s
Q.20 Radius of a capillary tube is 2 × 10
–3
m. A liquid of weight
6.28 × 10
–4 
N may remain in the capillary tube then the
surface tension of liquid will be
(a) 5 × 10
–3
 N/m (b) 5 × 10
–2
 N/m
(c) 5 N/m (d) 50 N/m
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a)  1, 2 and 3 are correct (b)  1 and 2 are correct
(c)  2 and 4 are correct (d)  1 and 3 are correct
4
DPP/ P 21
Q.21 The temperature at which the surface tension of water is
zero
(1) 370°C
(2) 0°C
(3) Slightly less than 647 K
(4) 277 K
Q.22 Which of the following statements are true in case when
two water drops coalesce and make a bigger drop?
(1) Energy is released.
(2) Energy is absorbed.
(3) The surface area of the bigger drop is smaller than the
sum of the surface areas of both the drops.
(4) The surface area of the bigger drop is greater than the
sum of the surface areas of both the drops.
Q.23 An air bubble in a water tank rises from the bottom to the
top. Which of the following statements are true?
(1) Bubble rises upwards because pressure at the bottom
is greater than that at the top.
(2) As the bubble rises, its size increases.
(3) Bubble rises upwards because pressure at the bottom
is less than that at the top.
(4) As the bubble rises, its size decreases.
DIRECTIONS (Q.24-Q.25) : Read the passage given below
and answer the questions that follows :
There is a small mercury drop of radius 4.0mm. A surface P of area
1.0 mm
2
 is placed at the top of the drop. Atmospheric pressure =
10
5
 Pa.  Surface tension of mercury = 0.465 N/m.  Gravity ef-
fect is negligible.
Q.24 The force exerted by air on surface P is
(a) 0.1 N (b) 1.0023 N (c) 10
5
 N (d) 1.0 N
Q.25 The force exerted by mercury drop on the surface P is
(a) 0.1 N (b) 1.0023 N
(c) 0.00023 N (d) 0.10023 N
DIRECTIONS (Qs. 26-Q.28) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.26 Statement-1 : A large soap bubble expands while a small
bubble shrinks, when they are connected to each other by a
capillary tube.
Statement-2: The excess pressure inside bubble (or drop)
is inverse ly proportional to the radius.
Q.27Statement-1 : Bernoulli’s theorem holds for
incompressible, non-viscous fluids.
Statement-2 : The factor 
2
2
v
g
 is called velocity head.
Q.28 Statement-1 : The velocity increases, when water flowing
in broader pipe enter a narrow pipe.
Statement-2 : According to equation of continuity , product
of area and velocity is constant.