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 energy and its forms introduction to work work introduction to work and energy

Rahul took a wooden cube of volume $1000  {cm}^3$ and put it in water. He observed that $\displaystyle \frac{3}{5}th$ of its volume is below the level of water. Later, he floated the cube in a liquid of density $0.8  g  {cm}^{-3}$ and applied extra force on the cube to completely submerge it in the given liquid. Calculate how much extra force Rahul applied on the cube.

  1. 2 N

  2. 8 N

  3. 6 N

  4. 4 N
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Volume = 1000 cm^3. In water (density 1), 3/5 submerged means weight = 0.6 * 1000 * 1 = 600g = 6N. In liquid (density 0.8), buoyant force when fully submerged = 1000 * 0.8 = 800g = 8N. Since weight is 6N, the extra force required to submerge it is 8N - 6N = 2N.

Multiple choice physics measurement and effects of heat thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

The coefficient of volume expansion of liquid is $\gamma$. The fractional change in its density for $\triangle T$ rise in temperature is ?

  1. $\gamma \triangle T$
  2. $\dfrac{\triangle T}{\gamma}$
  3. $1+\gamma \triangle T$
  4. $1-\gamma \triangle T$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

On thermal expansion,

Volumetric expansion is given by
$V=V _0(1+\gamma \Delta T)$. . . . . . . .(1)
We know that, density, $d=\dfrac{mass}{volume}$
$d=\dfrac{m}{V}$
where, $m=$ constant
$d\propto \dfrac{1}{V}$
Density of the liquid varies as

$d=d _0(1+\gamma \Delta T)$
$d=d _0+d _0\gamma \Delta T$
Fractional change in density is 
$\dfrac{d-d _0}{d _0}=\gamma \Delta T$
$\dfrac{\Delta d}{d _0}=\gamma \Delta T$
The correct option is A.

Multiple choice physics kinetic theory of gases thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

A glass capillary tube sealed at both ends is 100cm long. It lies horizontally with the middle 10cm containing mercury. The two ends of the tube which are equal in length contain air at $27 ^ { 0 } \mathrm { C }$ at a pressure of 76cm of Hg. Now the air column at one end of the tube is kept at $0 ^ { 0 } \mathrm { C }$ and the other end is maintained at $127 ^ { \circ } C$. Calculate the pressure of the air column at $0 ^ { \circ } \mathrm { C }$. (Neglect the change in volume of Hg and glass).

  1. $25$ cm of HG
  2. $35$ cm of HG
  3. $55$ cm of HG
  4. $85$ cm of HG
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the ideal gas law PV = nRT, since the amount of gas and the total volume are constant, we relate the pressures and temperatures. The pressure of the gas at 0C (273K) and 127C (400K) must satisfy the condition that the total length of the air columns remains constant (90cm total). Solving the system of equations for the pressure P leads to 35 cm of Hg.

Multiple choice physics kinetic theory of gases thermal expansion in gases thermal expansion of fluids volume elasticity constant of gases

Solid floating in a liquid . On decreasing the temperature solid sinks into the liquid . If ${ \Upsilon  } _{ l }\quad and\quad { \alpha  } _{ s }$ are volume expansion coefficient of liquid and linear expansion coefficient of solid , then :

  1. ${ \Upsilon } _{ l }\quad <\quad 3{ \alpha } _{ s }$
  2. ${ \Upsilon } _{ l }\quad >\quad 3{ \alpha } _{ s }$
  3. ${ \Upsilon } _{ l }\quad =\quad 3{ \alpha } _{ s }$
  4. ${ \Upsilon } _{ l }\quad =\quad 2{ \alpha } _{ s }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A solid floats if its density is less than the liquid density. If the solid sinks upon cooling, it means the density of the solid increased more than the density of the liquid, or the liquid density decreased relative to the solid. Since volume expansion coefficients are related to density changes, the condition for the solid to sink is that the liquid's volume expansion coefficient is greater than the solid's volume expansion coefficient (3 * alpha).

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

Kerosene floats on water because :

  1. kerosene has more density

  2. kerosene has less energy

  3. densities of water and kerosene are equal

  4. water has more density
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Water is denser than kerosene. The density of water is $1000kg/m^3$ and kerosene is $810kg/m^3$

when something is less dense than the water then it floats on water. Thus kerosene floats on water.

Option D is correct.

Multiple choice capacitance of an isolated spherical conductor capacitance of isolated bodies capacitance physics

1000 drops ofwater each of radius r and charged to a potential V coalesce together to form a big drop. The potential of big drop will be

  1. 10 V

  2. 100 V

  3. 1000V
  4. $\displaystyle \frac{V}{100}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Vol. of the big drop =1000 *vol. of each small drop
$\displaystyle \frac{4}{3} \pi R^3 = 1000\times \frac{4}{3} \pi r^3$
$\Rightarrow R^3 = (10r)^3$
$\Rightarrow $ R =10r
Potential of each charged sphere for small drop, V = $\displaystyle \frac{q}{c}$
$\therefore$ Potential for the big drop = $1000 \displaystyle \frac{q}{C}$
We have, $C= 4 \pi \epsilon _0 R = 4 \pi \epsilon _0 \times 10 r$
$\therefore$ Potential of the big drop 
=$\displaystyle \frac{1000}{10} . \frac{q}{4 \pi \epsilon _0 r} =100V$

Multiple choice maths how big? how heavy? measuring volume volume of solids volume of cube and cuboid

A sphere of radius 2 cm is put into water contained in a cylinder of radius 4 cm. If the sphere is completely immersed, the water level in the cylinder rises by __________________.

  1. Two cm
  2. $\displaystyle\frac{1}{3}\:cm$
  3. $\displaystyle\frac{1}{2}\:cm$
  4. $\displaystyle\frac{2}{3}\:cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Volume of sphere = (4/3) * pi * r^3 = (4/3) * pi * 2^3 = (32/3) * pi. Volume of water rise in cylinder = pi * R^2 * h = pi * 4^2 * h = 16 * pi * h. Equating: (32/3) * pi = 16 * pi * h, so h = 32 / (3 * 16) = 2/3 cm.

Multiple choice maths how big? how heavy? measuring volume volume of solids volume of cube and cuboid

If \$210m^\$ of sand be thrown into a tank \$12\$m long and \$5\$m wide, find how much the water will rise?

  1. $3.5$m
  2. $4$m
  3. $7$m

  4. Data inadequate
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Assuming '210m³' of sand, volume = 210 m³. Tank base area = 12 × 5 = 60 m². Rise in water level = 210/60 = 3.5 m. This matches option A. Options B and C are incorrect calculations.

Multiple choice fluid dynamics option b: engineering physics physics

Two identical lead shots are dropped at the same time in two glass jars containing water and glycerine. The lead shot dropped in glycerine descends slowly because:

  1. Viscous force is more in water than in glycerine

  2. Viscous force is more in glycerine than in water

  3. Surface tension is more in water

  4. Surface tension is more in glycerine
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Glycerine viscosity is 950 cP and water viscosity is 0.89 cP. We can see that glycerine has high viscosity. High viscous force of glycerine increases the time of drop of lead shot than in water.

Multiple choice fluid dynamics option b: engineering physics physics

When stirring of a liquid is stopped, the liquid comes to rest due to:

  1. surface tension

  2. gravity

  3. viscosity

  4. buoyancy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When stirring of a liquid is stopped, the liquid comes to rest due to viscosity of liquid. While stirring fluid at the axis moves faster in circular path whereas the fluid in contact with the walls does not move. So, the viscous drag force acting between the fluid layers tries to restrict the relative motion of them. So, by viscous drag force liquid comes to rest. 

Multiple choice fluid dynamics option b: engineering physics physics

When an object is dropped into a fluid, the extent of splash, due to buoyant force of fluid, depends on:

  1. sliding friction

  2. rolling friction

  3. fluid friction

  4. static friction
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The splash, due to buoyant force of a fluid depends on fluid friction.

Multiple choice fluid dynamics option b: engineering physics physics

Two spheres $A$ and $B$ fall through the same viscous fluid. $A$ and $B$ have the same density and $B$ has the larger radius.
Then,

  1. A has the larger terminal velocity

  2. A and B have the same terminal velocity

  3. B has the larger terminal velocity

  4. Insufficient information is given to reach a conclusion.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Two spheres $A$ and $B$ fall through the same viscous fluid $A$ and $B$ have  the same density and $B$ has the larger radius the $B$ has the larger terminal velocity.

$\therefore $ Option $C$ is correct.