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 viscosity option b: engineering physics properties of matter physics

An air bubble of radius $1 mm$ moves up with uniform velocity of $0.109ms^{-1}$ in a liquid column of density $14.7 \times 10^{3} kg/m^{3}$, then coefficient of viscosity will be ($g = 10ms^{-2}$)

  1. $1.3 Pa- s$
  2. $300 Pa -s$
  3. $15 Pa- s$
  4. $150 Pa- s$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If the bubble is moving up with uniform velocity, the frictional force acting downwards is equal to the buoyant force acting upwards.

$\implies V\rho g=6\pi\eta rv$
$\implies \eta=\dfrac{V\rho g}{6\pi rv}$
$=0.3Pa.s$

Multiple choice viscosity option b: engineering physics properties of matter physics

A solid ball of density half that of water falls freely under gravity from a height of 19.6 m and then enters the water. Up to what depth will the ball go? How much time will it take to come again to the water surface. Neglect air resistance and viscosity effects in water. ($
g=9.8 \mathrm{ms}^{-2}
$)

  1. 4 s

  2. 8 s

  3. 6 s

  4. 2 s
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The ball falls 19.6 m, reaching velocity v = sqrt(2gh) = sqrt(2 * 9.8 * 19.6) = 19.6 m/s. In water, the buoyant force exceeds gravity (density is half of water), so it decelerates. The time to stop and return is calculated using the effective acceleration in water.

Multiple choice viscosity option b: engineering physics properties of matter physics

A spherical ball of radius $3\times 10^{-4}\ m$ and density $10^{4}\ kg\ m^{-3}$ falls freely under gravity through a distance $h$ before entering a tank of water. If after entering the water, the velocity of the ball does not change, then the value of $h$ is (Given, $viscosity >of> water=9.8\times 10^{-6}\ Nsm^{-2}$ and $\rho _{water}=10^{3}\ kgm^{-3}$)

  1. $1650\ m$
  2. $165\ m$
  3. $1050\ m$
  4. $105\ m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If the velocity does not change upon entering water, the drag force must balance the net weight in water. F_drag = (m_ball - m_displaced) * g. Using Stokes' Law for F_drag and equating, we solve for the velocity v, then use v^2 = 2gh to find h.

Multiple choice physics learning how to measure measurement of area and volume measurement of volume measurement of area, volume and density

Find the volume of a ring immersed in water ,increasing the level from 55.2 ml to 75.3 ml.

  1. $20.1\ ml$
  2. $29\ ml$
  3. $10.1\ ml$
  4. $14.1\ ml$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Initial volume level   $V _i = 55.2 \ ml$
Final volume level   $V _f = 75.3 \ ml$
Thus, volume of ring    $V = V _f-V _i$
$\implies \ V = 75.3-55.2 = 20.1 \ ml$

Multiple choice physics learning how to measure measurement of area and volume measurement of volume measurement of area, volume and density

The density of steel rod is $7850\ kg/m^3$, its mass is $5\ kg$.Find its volume?

  1. $7.36\times 10^{-4}\ m^3$
  2. $36\times 10^{-4}\ m^3$
  3. $6.36\times 10^{-4}\ m^3$
  4. $6\times 10^{-4}\ m^3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mass of steel rod $m = 5 \ kg$
Density of steel rod   $d = 7850 \ kg/m^3$
Volume of steel rod  $V = \dfrac{m}{d}$
$\implies \ V = \dfrac{5}{7850} = 6.36\times 10^{-4} \ m^3$

Multiple choice physics learning how to measure measurement of area and volume measurement of volume measurement of area, volume and density

The volume of water in a measuring cylinder is 55 mL When a stone tied to a string is immersed in the water the water level rises to 83 mL. Find the volume of the stone

  1. $28ml^2$
  2. $28ml$
  3. $38ml$
  4. $28m^2l$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Initial level of water  $v _i = 55 \ ml$
Final level of water  $v _f = 83  ml$
Volume of stone  $V _{stone} = V _f - V _i = 83 - 55 = 28 \ ml$
Multiple choice physics learning how to measure measurement of area and volume measurement of volume measurement of area, volume and density

A cubic metre of water at $0^o$C is solidified into ice, density of ice is $0.96$ of water at $0^o$C. Which of the following deductions are true?
$1$. Water expands when solidified.
$2$. Ice will float in water at $0^o$C with half its volume above the surface.
$3$. Density of all liquids are higher than its density when solidified.

  1. $3$ only
  2. $2$ only
  3. $1$ only
  4. $1$ and $2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When water freezes into ice, its density decreases, meaning its volume increases (it expands). This expansion is a unique property of water. Statement 1 is true. Statement 2 is false because ice floats with about 90% of its volume submerged, not 50%. Statement 3 is false as a general rule.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A rectangular block is $10\ cm \times 10\ cm \times 15\ cm$ in size is floating in water with $10\ cm$ side vertical. If it floats with $15\ cm$ side vertical, then the level of water will

  1. $Rise$
  2. $Fall$
  3. $Remain\ same$
  4. $Change\ according\ to\ density\ of\ block$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Archimedes' principle, a floating object displaces a weight of fluid equal to its own weight. Since the weight of the block remains constant regardless of its orientation, the weight (and thus the volume) of the water displaced remains the same, so the water level does not change.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A boat having some iron pieces is floating in a pond. If iron pieces are thrown in the liquid then level of liquid 

  1. Increases

  2. Decreases

  3. May increase or decrease

  4. Neither increases nor decreases
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the iron pieces are in the boat, they displace a volume of water equal to their weight divided by the density of water. When thrown into the water, they sink and displace only a volume of water equal to their own volume. Since the density of iron is much greater than that of water, the volume displaced when submerged is less than the volume displaced when floating, causing the water level to decrease.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A hollow metal container floats in water, because it displaces _____ weight of water than/as its own weight.

  1. more

  2. less

  3. same

  4. can't say
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

FALSE
If hollow metal container  displaces more weight of water than its own weight it will sink.
Because, we know that by Archimedes principle, the weight of water displaced should be equal to the weight of the part submerged in water. If the weight is greater than the weight of the object, it will sink.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A body of density 5.34  $ \displaystyle g/cm^{3} $ when immersed in water (density 1.0$ \displaystyle g/cm^{3} $ ) will 

  1. float

  2. sink

  3. rise

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 

Any solid floats on water if its density is less than the density of water(i.e. 1).So, it will sink.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A piece of iron [density 7.6$ \displaystyle gcm^{-3} $] sinks in mercury [density 13.6 $ \displaystyle gcm^{-3} $]. State whether true or false.

  1. True

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

Since condition for sinking of a body of density $\sigma $ in a liquid of density S is 

                  $\sigma >S.$
& Since iron of density 7.69/cc is less lighter than density of mercury (density 13.6g/cc). Hence iron will float on mercury.