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 forces and matter pressure in fluids pressure in liquids introduction to pressure

Liquid rise in a syringe when its piston is pulled up due to 

  1. Atmospheric pressure

  2. Inertia of motion

  3. Inertia of rest

  4. Conservation of momentum
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the piston is pulled up, air pressure inside syringe reduces because of increase in volume. While pressure outside syringe is more than that. So, it pushes liquid into syringe.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

What is the relationship between liquid pressure and the depth of a liquid?

  1. Directly proportional

  2. Inversely proportional

  3. Linear

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The relationship between liquid pressure and the depth of a liquid:

Pressure at depth 'h' = density of fluid $\times $ acceleration due to gravity 'g' $\times $  depth 'h'.
Pressure is directly proportional to depth. If we triple the depth, we triple the pressure.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

The pressure a liquids exerts against the sides and bottom of a container depends on the 

  1. atmospheric pressure

  2. surface area

  3. volume of container

  4. density and depth of liquid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\because p = h\times d\times g$
where, p = pressure, h = depth (height), d = density,  g = acceleration due to gravity = constant.

So, pressure depends on density and depth of liquid.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

A tank $5\ m$ high is half filled with water and then is filled to the top with oil of density $0.85\ g\ cm^{-3}$. The pressure at the bottom of the tank, due to these liquids, is

  1. $1.85\ g$
  2. $89.25\ g\ dyne\ cm^{-3}$
  3. $462.5\ g\ dyne\ cm^{-2}$
  4. $500\ g\ dyne\ cm^{-2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We know that the pressure increases as we go deep into a liquid. The relation is given by $\Delta P = \rho g\Delta h$


Given that the tank is half filled with water and half with oil.
Thus, $h _\textrm{oil} = 2.5\textrm{ m}$ and $h _\textrm{water} = 2.5\textrm{ m}$

Thus, pressure at the bottom of the tank is $\Delta P = \Delta P _\textrm{oil} + \Delta P _\textrm{water} = 0.85\times 250g + 1\times 250g=462.5g \textrm{ dyne cm}^{-2}$

Multiple choice physics pressure pressure in fluids pressure in liquids introduction to pressure

The Pressure at any point in the liquid is proportional to :

  1. The density of liquid.

  2. The depth of point below the surface.

  3. The acceleration due to gravity.

  4. All the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pressure at any point in the liquid $(P)=hdg$
i.e., $P\alpha h$
(depth of point below the surface)
$\alpha d$ (density of liquid)
$\alpha g$ (acceleration due to gravity)

Multiple choice physics pressure pressure in fluids pressure in liquids introduction to pressure

Liquid pressure at a point in a liquid does not depend on the :

  1. Density of liquid

  2. Shape of the vessel in which the liquid is kept

  3. Depth of the point from the surface

  4. Acceleration due to gravity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

pressure in a fluid = $\rho gh $ 

so clearly it is independent of the shape of the vessel in which the liquid is kept .
hence option (B) is correct .

Multiple choice physics fluids pressure in fluids pressure in liquids introduction to pressure

Pressure at a point inside the liquid does not depend upon :

  1. The depth of the point below the surface of the liquid.

  2. The nature of the liquid.

  3. The acceleration due to gravity at that point.

  4. The shape of the container.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pressure at a point inside the liquid $(P)=hdg$
Hence, it depends on the depth of the point below the surface of the liquid the acceleration due to gravity at that point and on the nature of the liquid but not on the shape of the containing liquid.

Multiple choice physics properties of material substances poisson ratio poisson's ratio elastic energy

A cube of wood supporting $200 gm$ mass just in water $(\rho =1g/cc)$. When the mass is removed, the cube rises by $2cm$. The volume of cube is

  1. $1000 cc$
  2. $800cc$
  3. $500 cc$

  4. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Let the edge of cube be $L$ when mass is on the cube of wood 
$200g+{ L }^{ 3 }{ d } _{ wood }g={ L }^{ 3 }{ d } _{ water }g$
$\Rightarrow { L }^{ 3 }{ d } _{ wood }g={ L }^{ 3 }{ d } _{ water }g$
$\Rightarrow { L }^{ 3 }{ d } _{ wood }g={ L }^{ 3 }{ d } _{ water }g-200g$
$\Rightarrow { L }^{ 3 }{ d } _{ wood }={ L }^{ 3 }d-200$
When mass is removed
${ L }^{ 3 }{ d } _{ wood }-\left( L-2 \right) { L }^{ 2 }{ d } _{ water }\quad \longrightarrow \left( 2 \right) $
From $(1)$ and $(2)$
${ L }^{ 3 }{ d } _{ water }-200=\left( L-2 \right) { L }^{ 2 }{ d } _{ water }$
But ${ d } _{ water }=1$
$\therefore$    ${ L }^{ 3 }-200={ L }^{ 2 }\left( L-2 \right) $
$\therefore$    $L=10cm$.
Multiple choice physics units and measurement: error analysis significant figures significant figures and rounding of digits units and measurements

Relative density of a metal may be found with the help of spring balance. In air the spring balance reads $(5.00\pm 0.05)$ N and in water it reads $(4.00\pm 0.05)$N. Relative density would be:

  1. $(5.00\pm 0.05)N$
  2. $(5.00\pm$ 11%)
  3. $(5.00\pm 0.10)$
  4. $(5.00\pm$ 6%)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Relative density $=\dfrac {\text {Weight of body in air}}{\text {Loss of weight in water}}$$=\dfrac {5.00}{5.00-4.00}=\dfrac {5.00}{1.00}$

$\dfrac {\Delta \rho}{\rho}\times 100=\left (\dfrac {0.05}{5.00}+\dfrac {0.05}{1.00}\right )\times 100$
                    $=(0.01+0.05)\times 100$
                    $=0.06\times 100$
                    $ =6$% 
$\therefore$ Relative density $=5.00\pm$ 6%

Multiple choice physics units and measurement: error analysis significant figures significant figures and rounding of digits units and measurements

Find density when a mass of 9.23 kg occupies a volume of $\displaystyle 1.1m^{3}$ with due regard to significant figures.

  1. $\displaystyle 8.4 kg/m^{3}$
  2. $\displaystyle 8.39 kg/m^{3}$
  3. $\displaystyle 8.3 kg/m^{3}$

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mass $= 9.23\ kg$ .... 3 significant figures

Volume $= 1.1\  m^3$ .... 2 significant figures

Therefore, $density = mass/volume = 8.4\ kg/m^3$ 

Multiple choice physics units and measurement: error analysis significant figures significant figures and rounding of digits units and measurements

The mass of a beaker is found to be ($10.1 \pm 0.1)gm $ when empty and $(17.3 \pm 0.1)gm$ when partially filled with a liquid. What is the best value for the mass of the liquid together with the possible limits of accuracy?

  1. $(7.2 \pm 0.2)gm$
  2. $(7.2 \pm 0.1)gm$
  3. $(7.1 \pm 0.2)gm$
  4. $(7.2 \pm 0.3)gm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here mass of the liquid , $m=m _2-m _1=17.3-10.1=7.2 gm$

So the relative error, $\dfrac{\Delta m}{m}=\pm\left[\dfrac{\Delta m _1}{m _1}+\dfrac{\Delta m _2}{m _2}\right]$
or $\Delta m=\pm\left[\dfrac{\Delta m _1}{m _1}+\dfrac{\Delta m _2}{m _2}\right]\times m=\pm[0.1/10.1+0.1/17.3]\times 7.2=\pm 0.1 gm$
Thus mass of liquid with possible accuracy $=(7.2\pm 0.1) gm$

Multiple choice biology simple nutrients into cells blood and its components components of blood composition of blood

Plasma has water to the extent of _____________.

  1. $80\%$
  2. $60\%$
  3. $70\%$
  4. $90\%$ or more
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Plasma, which is 92 percent water, constitutes 55 percent of blood volume. Plasma contains albumin (the chief protein constituent), fibrinogen (responsible, in part, for the clotting of blood), and globulins (including antibodies).


So, the correct answer is '90%'.