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

A barometer tube reads $76$ $cm$ of mercury. If the tube is gradually inclined at an angle of $60 ^ { \circ }$ with vertical, keeping the open end immersed in the mercury reservoir, the length of the mercury column will be  

  1. $152 \mathrm { cm }$
  2. $76 \mathrm { cm }$
  3. $\dfrac{76cm}{sin30^o}$
  4. $38 \mathrm { cm }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The vertical height of the mercury column in a barometer is independent of the tube's inclination, provided the reservoir is open to the atmosphere. The length of the mercury column along the tube will increase, but the vertical height remains 76 cm.

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

The temperature of an air bubble while rising from bottom to surface of a lake remains constant but its diameter is doubled if the pressure on the surface is equal to h meter of mercury column and relative density of mercury is p then the depth of lake in metre is

  1. $2\rho h$
  2. $4\rho h$
  3. $8\rho h$
  4. $7\rho h$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using Boyle's Law: P1V1 = P2V2. P1 = P_atm + rho_w*g*h. P2 = P_atm. Since diameter doubles, volume increases 8 times. P_atm + rho_w*g*h = 8 * P_atm. h = 7 * P_atm / (rho_w*g). Given P_atm = rho_m*g*h_m, we get h = 7 * (rho_m/rho_w) * h_m = 7 * rho * h.

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

The pressure of water at bottom in a lake is 3/2 times that at half depth where the water barometer reads $10$ m. The depth of the lake is:

  1. $15$ m

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

Let the point at half depth be $x,$

$P _1=P+dgx$

Let the depth of lake be $2x$,

$P _2=P+dg2x$

$P _2=3/2×P1$

$2P _2=3P1$

$2 (P+dg2x)=3 (P+dgx)$

$2P+4dgx=3P + 3dgx$

$P=dgx$

$x=P/dg$

$x=10^5/10000 (d=10^3kg/m^3) (P=10^5pa)$

But depth of lake is $2x$

$2x=2×10=20m$

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 chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

In froth floatation process, gangue particles are wetted by pine oil.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Froth flotation is a process to purify sulfide ores, in presence of pine oil. The oil acts as hydrophobic agent and forms froth with hydrophobic impurities (gangue) which is skimmed off from the surface leaving behind the concentrated mineral.
Wet pine oil is used in froth flotation process because it does not have an affinity towards water (because of the hydrophobic chemicals as its constituents)and it attracts impurities which can be washed away.
Hence, it is true.
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.