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 upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

An object having relative density 0.56 is dropped in water. Will it float or sink in water?

  1. Sink

  2. Float

  3. Depends on the density of water

  4. Unsure
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Explanation: the relative density of water is 1 and that of the object is less than 1. Thus the upthrust experienced by the object will be more than the weight of the object making it float on the surface of water.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A body of density equal to density of fluid is sinking at speed of $1 m/s$ at $t=0$. What is distance covered by object in $1s$? 

  1. $0.5m$
  2. $1m$
  3. $0.75m$
  4. $0.875m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Upthrust = weight of the body since density of body equals density of fluid

Hence, Net force $= 0$ and acceleration$ = 0$
Distance = speed x time$ = 1m$

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

Analyse the given statements and choose the correct option.
Statement I: The buoyant force of water on a submerged wooden cube is greater than the buoyant force of water on a steel cube of equal volume.
Statement II: The buoyant force on a body is equal to the weight of the liquid displaced by the body.

  1. Both statement I and statement II are correct and statement II is the correct explanation of statement I

  2. Both statement I and statement II are correct, but statement II is not the correct explanation of statement I

  3. Statement I is correct, but statement II is incorrect

  4. Statement I is incorrect, but statement II is correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since buoyant force experienced by a body is equal to weight of liquid displaced by the body. Hence it remains same for all the bodies of equal volume.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A metal wire of density $d$ floats, in a liquid of surface tension $\sigma$, in the horizontal position. The maximum radius of the wire so that it may not sink is

  1. $\sqrt{\dfrac{2\sigma}{\pi d g}}$
  2. $\sqrt{\dfrac{3\sigma}{\pi d g}}$
  3. $\sqrt{\dfrac{5\sigma}{\pi d g}}$
  4. $\sqrt{\dfrac{7\sigma}{\pi d g}}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

When a ship floats on water :

  1. it displaces no water

  2. the mass of water displaced is equal to the mass of the ship

  3. the mass of water displaced is lesser than the mass of the ship

  4. the mass of water displaced is greater than the mass of the ship
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the law of flotation, a floating object displaces a weight of fluid equal to its own weight. Therefore, the mass of the displaced water equals the mass of the ship.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A boat 3 m long and 2 m wide is floating in a lake. When a man climbs over it, it sinks 1 cm further into water. The mass of the man is:

  1. 60 kg

  2. 64 kg

  3. 70 kg

  4. 72 kg
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\delta Vg$=Weight of mass.

$\begin{array}{l} 1000\times \left( { 3\times 2\times \frac { 1 }{ { 100 } }  } \right) \times 10=mg \ m=60kg \end{array}$
$ \therefore$ Option $A$ is correct.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A ball floats on the surface of water in a container exposed to the atmosphere. Volume $V _{1}$ of its volume in inside the water. If the container is now covered and the air is pumped out. Now let $V _{2}$ be the volume now immersed in water. Then

  1. $V _{1}=V _{2}$
  2. $V _{1}>V _{2}$
  3. $V _{2}>V _{1}$
  4. $V _{2}=0$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The buoyant force is equal to the weight of the displaced water. Since the weight of the ball and the density of the water do not change when the air is removed, the volume of water displaced remains the same.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A vessel in the shape of a hollow hemisphere surmounted by a cone is held with the axis vertical and vertex uppermost. If it be filled with a liquid so as to submerge half the axis of the cone in the liquid, and the height of the cone be double the radius of its base, find the value of $x$, where the resultant downward thrust of the liquid on the vessel is $x$ times the weight of the liquid that the hemisphere can hold.

  1. $15/8$
  2. $1/8$
  3. $5/8$
  4. $15/2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The resultant downward thrust is calculated by integrating the pressure over the wetted surface area. For a cone with height h=2r, submerging half the axis means the liquid height is r. The calculation involves the weight of the displaced liquid and the pressure at the base, leading to the ratio 5/8.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A wooden cube floating in water supports a mass m = 0.2 kg on its stop. When the mass is removed the cube rises by 2 cm. The side of the cube is - (density of water $10^3 kg/m^3$)

  1. 6 cm

  2. 12 cm

  3. 8 cm

  4. 10 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Cube is floating, therefore
Weight of liquid displaced $=$ Weight of cube
let  the volume of liquid displaced $= V$
Density of liquid $= \rho$
Mass of cube $= M$

Then,

$(M+m)g=\rho v g$

$\implies M+m=\rho v$       ............(1)

When mass is removed, cube reise by $l=2\,cm$

Therefore,

$Mg=(V-lA)\rho g$

where, $AS$ is the are of face of cube

$\implies M=\rho(V-lA)$          .................(2)

Eliminating $M$ by subtracting (2) from (1)

$m=\rho l A$

$\implies A=\dfrac{m}{\rho l}$

Let side of cube $=a$

Then,

$a^2=A=\dfrac{m}{\rho l}$

$\implies a=\sqrt{\dfrac{m}{\rho l}}$

If liquid is water, then $\rho=1000\,kg/m^3$

$I=0.02\,m$ (given)

$m=0.2\,kg$ (given)

Putting these value, we get $a=0.1\,m=10\,cm$