Physics

Fluid Mechanics

673 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 physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

Two communicating vessels contain mercury. The diameter of one vessel is four times larger than the diameter of the other. A column of water of height $h _0=70$ cm is poured into the left hand vessel (the narrower one). How much will be mercury level rise in the right hand vessel? ( Specific density of mercury= $13.6$)

  1. $0.3$ cm
  2. $0.7$ cm
  3. $0.1$ cm
  4. $1.0$ cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

An air bubble doubles its radius on rising from the bottom of water reservoir to the surface of water in it. If the atmospheric pressure is equal to $10 m $ of water, the height of water in the reservation s- 

  1. $ 10m $
  2. $20 m$
  3. $70 m$
  4. $80 m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using Boyle's Law: P1V1 = P2V2. P1 = P_atm + rho*g*h. P2 = P_atm. Volume increases 8 times (2^3). P_atm + rho*g*h = 8 * P_atm. h = 7 * P_atm / (rho*g). Since P_atm = 10m of water, h = 7 * 10m = 70m.

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

A cubical block of steel each side '$\ell $' is floating in mercury in a vessel. The densities of steel and mercury are ${ p } _{ s }\quad and\quad { p } _{ m }$ .The height of block above the mercury level is given by.

  1. $\ell \left( 1+\dfrac { { p } _{ s } }{ { p } _{ m } } \right) $
  2. $\ell \left( 1-\dfrac { { p } _{ s } }{ { p } _{ m } } \right) $
  3. $\ell \left( 1+\dfrac { { p } _{ m } }{ { p } _{ s } } \right) $
  4. $\ell \left( 1-\dfrac { { p } _{ m } }{ { p } _{ s } } \right) $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

By Archimedes' principle, the weight of the block equals the weight of the displaced mercury. rho_s * L^3 * g = rho_m * (L^2 * (L - h)) * g. Solving for h (height above surface) gives h = L * (1 - rho_s/rho_m).

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

A flask of volume $10^3cc$ is completely filled with mercury at $0^oC.$ The co-efficient of cubical expansion of mercury is $180\times10^{-6} /^oC$ at that of glass is $40\times10^{-6}/^oC.$ If flask is placed in boiling water at $100^oC,$ how much mercury will overflow   

  1. $7cc$
  2. $14cc$
  3. $21cc$
  4. $28cc$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The overflow volume is given by V * (gamma_mercury - gamma_glass) * delta_T. Overflow = 1000 * (180 - 40) * 10^-6 * 100 = 1000 * 140 * 10^-4 = 14 cc.

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

By sucking through a straw, a student can reduce the pressure in his lungs to $750 mm$ of Hg (density = $\displaystyle 13.6{ gm }/{ { cm }^{ 3 } }$). Using the straw, he can drink water from a glass upto a maximum depth of: 

  1. $10 cm$
  2. $75 cm$
  3. $13.6 cm$
  4. $1.36 cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pressure difference created $= 10 mm$ of Hg 
This must be equal to the pressure of water column being created in the straw. If height of water column be $h$

$h \rho g = \dfrac{10}{10} \times 13.6 g$
$hg \times 1 = 13.6 g$
$h = 13.6 cm$

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

What will be the pressure in pascal due to a mercury column of $76$cm. Density of mercury is $13.6$ g$cm^2$, $g=980$ cm$s^2$?

  1. $1.0129\times 10^5$Pa
  2. $1.0129\times 10^4$Pa
  3. $1.0129\times 10^3$Pa
  4. $1.0129\times 10^2$Pa
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 h$=76cm$

Pressure=?

Formula to be used : $P=hgd$

Where h = height of mercury column and

 d= density of mercury$=13.6 gm/cc$

acceleration due to gravity$=980 cm/s²$

$P=hgd=13.6\times 980\times 76=1012928dyne.cm²$

Multiple choice physics pressure in fluids and atmospheric pressure pressure in air introduction to atmospheric pressure devices to measure pressure
At sea level, the vertical height of mercury supported in the tube of simple barometer is ______ $cm$ above the mercury level in the bowl.
  1. $36$
  2. $76$
  3. $100$
  4. $7$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The height to which mercury rises in simple barometer is $76cm$.

This is the reason that  atmospheric pressure is often expressed as $76cm$ of Hg at sea level.

Multiple choice chemistry substances in the surroundings - their states and properties measurement of density properties of substances fundamental and derived units

Multiplying relative density by 100 we get density of liquid in   $ \displaystyle kg/m^{3} $

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Relative density of a substance is ratio of density of substance to that of water. Hence density of substance can be found by multiplying relative density with 1000$kg/{ m }^{ 3 }$ (density of water).

Multiple choice chemistry substances in the surroundings - their states and properties measurement of density properties of substances fundamental and derived units
The density of silver is 13.6 times greater than that of water.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know that, density of silver is $10.5 \times 10^3 \dfrac{kg}{m^3}$ and density of water is $1.00 \times 10^3 \dfrac{kg}{m^3}$.


Therefore, the density of silver is $10.5$ times greater than that of water.

Hence, the given statement is false.

Multiple choice chemistry substances in the surroundings - their states and properties measurement of density properties of substances fundamental and derived units

A vessel contains oil (density $= 0.8\ gm/cm^{3})$ over mercury (density $= 13.6\ gm/ cm^{3})$. A uniform sphere floats with half its volume immersed in mercury and the other half in oil. The density of the material of sphere in $gm/ cm^{3}$ is

  1. $3.3$
  2. $6.4$
  3. $7.2$
  4. $12.8$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A vessel contains oil density $=0.8gm/cm^3$

Mercury density $=13.6gm/cm^3$
Total weight is balanced by the displaced volumes of the two different fluids. Let it $s$ and volume id $v$ and te density is $n$.
Then the equilibrium condition should be
$v _{mg}=v/2(0.8)g+\cfrac{v}{2\times136g}\n=0.4+6.8=7.2gm/cm^3$