Physics

Fluid Mechanics

637 Questions

Fluid mechanics is a core physics topic that evaluates the principles of liquid pressure, buoyancy, density, and viscosity through complex numerical problems. The questions require calculating the volume of submerged objects, understanding hydraulic jumps, and applying fundamental fluid statics principles. It is a highly scoring subject for candidates preparing for technical and engineering competitive exams.

Liquid pressure and depthBuoyancy and densityVolume expansionHydraulic jump calculationsSurface tension mechanics

Fluid Mechanics Questions

Multiple choice surface tension physics surface energy of a liquid work done in stretching a liquid surface: surface energy of a liquid properties of matter

What is the change in surface energy, when a mercury drop of radius $R$ splits up into $1000$ droplets of radius $r$?

  1. $8\pi R^2T$
  2. $16\pi R^2T$
  3. $24\pi R^2T$
  4. $36\pi R^2T$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let Surface Tension be T.

Initial surface = $4\Pi { R }^{ 2 }$
Final Surface area = $1000\times 4\Pi { r }^{ 2 }$
& Initial Volume = final volume
$\dfrac { 4 }{ 3 } \Pi { R }^{ 3 }=1000\times \dfrac { 4 }{ 3 } \Pi { r }^{ 3 }$
R = 10r
So,
    Final surface area = $1000\times 4\Pi \times \dfrac { { R }^{ 2 } }{ 100 } =40\Pi { R }^{ 2 }$
So, Workdone = Change in Surface energy
                         = $T\Delta A=(40-4)\Pi { R }^{ 2 }T$
       $\boxed { Change\quad in\quad Surface\quad energy=36\Pi { r }^{ 2 }T } $.

Multiple choice

The volume of water in a piece of ice,

  1. Is equal to the surface area of the ice cube

  2. is equal to the volume of the ice below the water line

  3. is less than the volume of whole piece of ice

  4. Greater than (2*l*w)/(h), given the dimension of the ice
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Archimedes' principle states that a floating object displaces a weight of fluid equal to its own weight. Since ice is less dense than water, the volume of the displaced water is exactly equal to the volume of the submerged portion of the ice.

Multiple choice botany mineral nutrition in plants mechanism of absorption mineral absorption significance of transpiration

Which of the following statement is incorrect?

  1. Rise of water in a narrow tube is inversely proportional to the radius of the tube

  2. A water melon has over 92% water

  3. Dry plant material can imbibe ether but rubber cannot imbibe

  4. when water flows into thew cells and out of the cell and are in equilibrium, the cells are said to be flaccid
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

The surface tension and vapour pressure of water at $20^oC$ is 7.28$ \times10^{ -2 }$ N/m and $2.33 \times { 10 }^{ 3 }$ pa, respectively. What is the radius of the smallest spherical water droplet which can from without evaporating at $20^oC$ ?

  1. $5\times { 10 }^{ -4 }m$
  2. $6.25\times{10}^{-5}m$
  3. $9\times{10}^{-2}m$
  4. $3\times{10}^{-5}m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

 Work done in increasing the size of a soap bubble from a radius of $3\ cm$ to $5\ cm$ is nearly (Surface tension of soap solution$=0.03\ {Nm}^{-1}$):

  1. $0.2\pi\ mJ$
  2. $2\pi\ mJ$
  3. $0.4\pi\ mJ$
  4. $4\pi\ mJ$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work done = Surface Tension * Change in Surface Area. A soap bubble has two surfaces, so Area = 2 * (4 * pi * r^2) = 8 * pi * r^2. Change in Area = 8 * pi * (r2^2 - r1^2) = 8 * pi * (0.05^2 - 0.03^2) = 8 * pi * (0.0025 - 0.0009) = 8 * pi * 0.0016 = 0.0128 * pi m^2. Work = 0.03 * 0.0128 * pi = 0.000384 * pi J = 0.384 * pi mJ, which is approximately 0.4 * pi mJ.

Multiple choice intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

A capillary tube of radius $0.25\ mm$ is submerged vertically in water so that $25\ mm$ of its length outside water. The radius of curvature of the meniscus will be $(T = 7.5\times 10^{-3} N/m)$.

  1. $0.2\ mm$
  2. $0.4\ mm$
  3. $0.6\ mm$
  4. $0.8\ mm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$h= \dfrac{2T}{dgx}$

$h= \dfrac{2\times 7.5 \times {10}^-3} {1000 \times 10 \times d}$
$h=25mm$
$d= 0.6 mm$

Multiple choice commercial applications receding water table water and ocean conservation water resources and conservation water conservation and irrigation

What is density of water?

  1. 987kg/m3

  2. 997kg/m3

  3. 897kg/m3

  4. 797kg/m3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The density of pure water at standard atmospheric pressure and 4 degrees Celsius is approximately 1000 kg/m3. Among the provided choices, 997 kg/m3 is the closest scientific approximation for water at room temperature.

Multiple choice spectrophotometer, colorimeter and biosensor biochemical techniques bio-chemistry

Buoyant density centrifugation is carried out at

  1. 50,000g for 1-3 hours

  2. 50,000g for 20 hours

  3. 1,00,000g for 1-3 hours

  4. 1,00,000g for 20 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Buoyant density centrifugation (equilibrium centrifugation) requires long run times, often 20 hours or more, at high speeds (like 100,000g) to allow the particles to reach their isopycnic position in the gradient.

Multiple choice evs nature of things properties of materials grouping and classification of objects sorting materials into groups

The density of alcohol is 800 $ \displaystyle Kg/m^{3} $. Its relative density is:

  1. 8

  2. 0.8

  3. 0.08

  4. 800
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Relative density is the ratio of the density of the substance to the density of water.

We know that, density of water is $1 gm/cm^3   = 10^3 kg/m^3$

So, relative density of alcohol = $\dfrac{800}{1000}$ = $0.8$

Hence, option B is correct.
Multiple choice evs nature of things properties of materials grouping and classification of objects sorting materials into groups

A block of iron (density 9.8 $ \displaystyle g/cm^{3}) $ if added in mercury (density 13.6 $ \displaystyle g/cm^{3} $ ) will:

  1. sink

  2. float

  3. neither float nor sink i.e. remain suspended in mercury

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The average density of the object should be less than the density of the fluid in which the object has to float.


The density of object (iron) is less than the fluid (mercury).

Therefore, it will float.


Hence, option B is correct.