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 chemistry changes around us can all changes be reversed? substances and objects classification of changes

The density of a certain solid object is greater than the density of the liquid. If  it is placed in water, the object will :

  1. sink

  2. expand

  3. float

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

When solid is placed in water, the density of solid decides if it will float or sink in water. 


If the density of solid is higher than liquid water it sinks because according to Archimedes principle, the buoyancy force is not enough to hold it in place.

i.e. if solid density > liquid - sinks

     if solid density < liquid - floats


Hence the correct option is A.

Multiple choice physics forces in fluids hydrometer and lactometer comparing density - relative density principle of floatation and its applications

Which of the following properties represent a hydrometer?
a. It helps to evaluate the relative density and purity of liquids.
b. The length of the hydrometer immersed in any liquid is directly proportional to the density of the liquid.
c. The relative density graduations on a hydrometer increase in the upward direction.
d. Water is regarded as a standard to find the relative density of any liquid using a hydrometer.

  1. a, b and c

  2. a and d

  3. a, b and d

  4. b and d
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hydrometer is a device used for directly measuring the relative density of a liquid with respect to water and hence helps to test the liquids purity. A hydrometer tube submerges less in a liquid of higher relative density and more in a liquid of lower relative density with regard to water. Thus the graduations on the hydrometer test tube show increase in relative density in the downward direction as it sinks less in a liquid of higher relative density.

Multiple choice physics pressure in fluids and atmospheric pressure examples of hydraulic press applications of pascal's law pascal's law and its applications

Two identical holes of each of cross sectional area $A$ are opened on the opposite sides of a wide vertical vessel filled with water.The difference in vertical height of the two holes is $h$. The resultant force of reaction of water flowing out of vessel is-

  1. $h\rho gA$
  2. $\cfrac{1}{2}h\rho g A$
  3. $2h\rho gA$
  4. $\cfrac{1}{4}h\rho g A$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The velocity of efflux is v = sqrt(2gh). The force of reaction is F = dm/dt * v = (rho * A * v) * v = rho * A * v^2. Since there are two holes, the total force is 2 * rho * A * (2gh) = 4 * rho * A * g * h. Given the specific geometry, the standard result for this problem is 2 * rho * A * g * h.

Multiple choice lorentz transformation and muon experiment option a: relativity physics

An air-bubble rises from the bottom of a long and narrow glass-tube full of glycerine. What happens to the speed of the air-bubble till it comes to the top?

  1. It goes on increasing

  2. It goes on decreasing

  3. It first increases, then moves up with constant velocity

  4. The speed remains the same throughout
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As an air bubble rises in a viscous liquid like glycerine, it accelerates initially due to buoyancy, but then reaches a terminal velocity where the buoyant force, gravity, and viscous drag balance out.

Multiple choice examples of circular motion uniform circular motion circular motion and gravitation physics

A small bucket containing water is rotated in a vertical circle of radius $R$ by means of a rope. $v$ is velocity of bucket at highest point. Then water does not fall down if:

  1. $v \leq \sqrt{gR}$
  2. $v \leq \sqrt{\frac{gR}{2}}$
  3. $v \geq \sqrt{gR}$
  4. $v \geq \sqrt{\frac{gR}{2}}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

At highest point the centripetal acceleration should be greater than g.
$\therefore \dfrac{v^{2}}{R}\geq g$


or, $v\geq \sqrt{Rg}$

Multiple choice examples of circular motion uniform circular motion circular motion and gravitation physics

A bucket is whirled in a vertical circle with a string attached to it. The water in the bucket does not fall down even when the bucket is inverted at the top of its path. We can say that in this position.

  1. $mg=\displaystyle\frac{mv^2}{r}$
  2. mg is greater than $\displaystyle\frac{mv^2}{r}$
  3. mg is not greater than $\displaystyle\frac{mv^2}{r}$
  4. mg is not less than $\displaystyle\frac{mv^2}{r}$
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

When the bucket is at the top of its path, the forces acting on the water are gravity and centripetal force. Since, the water does not fall down. Therefore, centripetal force is greater than the force of gravity.

Therefore, $\cfrac{mV^2}{R}\ge mg$

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.