Fluid Mechanics Multiple Choice Questions – Buoyancy & Floatation

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1.

For a floating body, the buoyant force passes through the :

Dated: 19 Oct, 2018

Attempts: 104

Corrects: 34

Wrongs: 70

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centroid of the liquid displaced by the body
2. The condition of stable equilibrium for a floating body is :

Dated: 19 Oct, 2018

Attempts: 85

Corrects: 44

Wrongs: 41

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the metacenter M is above center of gravity G
3. A submerged body will be in stable equilibrium if :

Dated: 19 Oct, 2018

Attempts: 80

Corrects: 36

Wrongs: 44

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the center of buoyancy B is above G
4. The metacentric height of a floating body is :

Dated: 19 Oct, 2018

Attempts: 72

Corrects: 44

Wrongs: 28

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the distance between metacenter and center of gravity
5.

The point, through which the buoyant force is acting, is called :

Dated: 19 Oct, 2018

Attempts: 79

Corrects: 61

Wrongs: 18

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center of buoyancy
6.

The point, through which the weight is acting, is called :

Dated: 19 Oct, 2018

Attempts: 72

Corrects: 63

Wrongs: 9

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center of gravity
7.

The point, about which a floating body starts oscillating when the body is tilted, is called :

Dated: 19 Oct, 2018

Attempts: 70

Corrects: 50

Wrongs: 20

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meta-center
8.

The metacentric height GM is given by :

Dated: 20 Oct, 2018

Attempts: 57

Corrects: 0

Wrongs: 57

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\[GM = \frac{I}{V} - BG\]
9.

For a floating body, if the meta-center is above the center of gravity, the equilibrium is called :

Dated: 20 Oct, 2018

Attempts: 61

Corrects: 46

Wrongs: 15

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stable
10.

For a floating body, if the meta-center is below the center of gravity, the equilibrium is called :

Dated: 20 Oct, 2018

Attempts: 59

Corrects: 54

Wrongs: 5

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unstable
11.

For a floating body, if the meta-center coincides with the center of gravity, the equilibrium is called :

Dated: 20 Oct, 2018

Attempts: 60

Corrects: 52

Wrongs: 8

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neutral
12.

For a floating body, if the center of buoyancy is above the center of gravity, the equilibrium is called :

Dated: 20 Oct, 2018

Attempts: 57

Corrects: 33

Wrongs: 24

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stable
13. A balloon lifting in air follows the following principle :

Dated: 20 Oct, 2018

Attempts: 57

Corrects: 17

Wrongs: 40

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all are correct
14.

The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as :

Dated: 20 Oct, 2018

Attempts: 52

Corrects: 27

Wrongs: 25

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center of pressure
15.

The resultant upward pressure of a fluid on a floating body is equal to the weight of the fluid displaced by the body. This definition is according to :

Dated: 20 Oct, 2018

Attempts: 56

Corrects: 32

Wrongs: 24

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Archimedes' principle
16.

The resultant upward pressure of the fluid on an immersed body is called :

Dated: 20 Oct, 2018

Attempts: 54

Corrects: 39

Wrongs: 15

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buoyancy
17.

The conditions for the stable equilibrium of a floating body are :

Dated: 20 Oct, 2018

Attempts: 40

Corrects: 17

Wrongs: 23

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all are correct
18.

Metacentric height is given as the distance between :

Dated: 20 Oct, 2018

Attempts: 39

Corrects: 33

Wrongs: 6

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the center of gravity of the body and the meta-center
19.

The buoyancy depends on :

Dated: 20 Oct, 2018

Attempts: 54

Corrects: 28

Wrongs: 26

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mass of liquid displaced
20.

The center of gravity of the volume of the liquid displaced by an immersed body is called :

Dated: 20 Oct, 2018

Attempts: 46

Corrects: 35

Wrongs: 11

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center of buoyancy
21.

A piece of metal of specific gravity 13.6 is placed in mercury of specific gravity 13.6, what fraction of its volume is under mercury :

Dated: 20 Oct, 2018

Attempts: 41

Corrects: 26

Wrongs: 15

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whole of the metal piece will be immersed with its top surface just at mercury level
22.

An odd shaped body weighing 7.5 kg and occupying 0.01 m3 volume will be completely submerged in a fluid having specific gravity of :

Dated: 20 Oct, 2018

Attempts: 40

Corrects: 26

Wrongs: 14

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0.75
23.

The center of buoyancy of a submerged body :

Dated: 21 Oct, 2018

Attempts: 42

Corrects: 19

Wrongs: 23

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coincides with the centroid of the displaced volume of the fluid
24.

An object weighing 100 N in air was found to weigh 75 N when fully submerged in water. The relative density of the object is :

Dated: 21 Oct, 2018

Attempts: 42

Corrects: 13

Wrongs: 29

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\[\begin{array}{c} {W_{actual}} = 100{\rm{ N}}\\ {W_{apparent}} = 75{\rm{ N}}\\ {W_{apparent}} = {W_{actual}} - {F_b}\\ 75 = 100 - {F_b}\\ {F_b} = 25{\rm{ N}}\\ {F_b} = {\gamma _w} \times V \to 25 = {\gamma _w} \times V\\ S.{G_{object}} = \frac{{{\gamma _{object}}}}{{{\gamma _w}}}\\ S.{G_{object}} = \frac{{{\raise0.5ex\hbox{$\scriptstyle {{W_{actual}}}$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle V$}}}}{{{\gamma _w}}} = \frac{{{W_{actual}}}}{{{\gamma _w} \times V}} = \frac{{100}}{{25}}\\ S.{G_{object}} = 4 \end{array}\]
4.0
25.

An iceberg has 12 % of its volume projecting above the surface of the sea. If the density of sea water is 1025 kg/m3, the density of the iceberg is :

Dated: 21 Oct, 2018

Attempts: 27

Corrects: 16

Wrongs: 11

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\[\begin{array}{c} {V_{floating}} = 0.12V\\ {V_{immersed}} = 0.88V \to \frac{{{V_{immersed}}}}{V} = 0.88\\ {\rho _{sea}} = 1025{\rm{ kg/}}{{\rm{m}}^{\rm{3}}}\\ {F_b} = W\\ {\gamma _{sea}} \times {V_{immersed}} = {\gamma _{iceberg}} \times V\\ {\gamma _{iceberg}} = {\gamma _{sea}} \times \frac{{{V_{immersed}}}}{V}\\ {\rho _{iceberg}} = {\rho _{sea}} \times \frac{{{V_{immersed}}}}{V}\\ {\rho _{iceberg}} = 1025 \times 0.88\\ {\rho _{iceberg}} = 902{\rm{ kg/}}{{\rm{m}}^{\rm{3}}} \end{array}\]
902 kg/m3
26.

An object weighs 50 N in water and 80 N in an oil of relative density 0.80. Its volume in liters is :

Dated: 21 Oct, 2018

Attempts: 26

Corrects: 12

Wrongs: 14

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\[\begin{array}{c} {W_{app(water)}} = 50{\rm{ N}}\\ {W_{app(oil)}} = 80{\rm{ N}}\\ S.{G_{oil}} = 0.80\\ {W_{app(water)}} = {W_{actual}} - {F_{b(water)}}\\ 50 = {W_{actual}} - {\gamma _w} \times V\\ 50 = {W_{actual}} - 9810 \times V \to \\ {W_{app(oil)}} = {W_{actual}} - {F_{b(oil)}}\\ 80 = {W_{actual}} - {\gamma _{oil}} \times V\\ 80 = {W_{actual}} - 9810 \times 0.80 \times V \to \\ - \\ 30 = 9810 \times 0.20 \times V\\ V = {\rm{0}}{\rm{.0153 }}{{\rm{m}}^{\rm{3}}} \times 1000 = 15.3{\rm{ lit}} \end{array}\]
15.3
27.

A floating body displaces :

Dated: 21 Oct, 2018

Attempts: 43

Corrects: 14

Wrongs: 29

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a weight of liquid equal in magnitude to its own weight
28.

A metal block is thrown into a deep lake. As it sinks deeper in water, the buoyant force acting on it :

Dated: 21 Oct, 2018

Attempts: 45

Corrects: 17

Wrongs: 28

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increases
29.

When a block of ice floating on water in a container melts, the level of water in the container :

Dated: 21 Oct, 2018

Attempts: 41

Corrects: 9

Wrongs: 32

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falls
30.

When a ship enters sea from a river one can expect it :

Dated: 21 Oct, 2018

Attempts: 40

Corrects: 22

Wrongs: 18

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to rise a little
31.

Buoyant force is the :

Dated: 21 Oct, 2018

Attempts: 45

Corrects: 17

Wrongs: 28

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resultant hydrostatic force on a body due to fluid surrounding it
32.

A right circular wooden cone (specific gravity = 0.80) with a base diameter of 0.6 m and height of 0.8 m floats in water such that its axis is vertical and apex is downward. The immersed depth of cone is :

Dated: 22 Oct, 2018

Attempts: 22

Corrects: 4

Wrongs: 18

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0.743 m
33.

A 12 cm steel cube (relative density = 7.6) is submerged in a two layered fluid system. The bottom layer is mercury (relative density = 13.6) and the top layer is kerosene (relative density = 0.80). The height of the top surface of the cube above the interface of the two liquids is :

Dated: 22 Oct, 2018

Attempts: 19

Corrects: 9

Wrongs: 10

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5.63 cm
34.

Two cubes of size 1.0 m sides, one of relative density = 0.60 and another of relative density = 1.15, are connected by a weightless wire and placed in a large tank of water. Under equilibrium, the lighter cube will project above the water surface to a height of :

Dated: 23 Oct, 2018

Attempts: 19

Corrects: 3

Wrongs: 16

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25 cm
35.

If B = center of buoyancy, G = is the center of gravity and M = metacenter, of a floating body, the body will be in stable equilibrium if :

Dated: 23 Oct, 2018

Attempts: 26

Corrects: 23

Wrongs: 3

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M is above G
36.

In a floating body, I = moment of inertia of water line area about the longitudinal axis, V = volume of displaced fluid, B = center of buoyancy, G = center of gravity and M = metacenter. For stable equilibrium of this body :

Dated: 23 Oct, 2018

Attempts: 25

Corrects: 0

Wrongs: 25

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\[MG = \frac{I}{V} + BG\]
37.

A body is floating in a liquid as shown in the following figure. The center of buoyancy, center of gravity and metacenter are labeled as B, G and M respectively. The body is :

Fluid Mechanics MCQ - Q.51

Dated: 23 Oct, 2018

Attempts: 28

Corrects: 12

Wrongs: 16

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rotationally unstable
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