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 experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

According to the law of floatation weight  of floating body is -

  1. Equal to the weight of liquid displaced

  2. Equal to the volume of liquid displaced

  3. Is greater than the weight of liquid displaced

  4. Is less than the weight of liquid displaced
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Archimedes principle , weight of body in water or liquid is equal to the weight of the liquid displaced by it.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

The specific gravity of ice is $0.9$. The area of the smallest slab of ice of height $0.5\ m$ floating in fresh water that will just support a $100\ kg$ man is

  1. $1.5\ m^{2}$
  2. $2\ m^{2}$
  3. $3\ m^{2}$
  4. $4\ m^{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

wt. of man = 1000 N

wt. of ice = $0.9\times area\times 0.5N$
wt. of water = $1\times area\times 0.5N$
So, wt. of water = wt. of ice + wt. of man
      area $\times 0.5=area\times 0.9\times 0.5+2000$
      1 area = 20000 = ${ 2m }^{ 2 }$

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A rectangular boat floating in water has length 4 m and breadth 1.5 m. A person gets into the boat as a result of w which the boat sinks by 2 cm. Mass of the person is :

  1. 80 kg

  2. 100 kg

  3. 120 kg

  4. 92 kg
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given,

$l=4m$
$b=1.5m$
$h=2cm=0.02m$
Volume, $V=lbh$
$V=4\times 1.5\times 0.02 =0.12m^3$
Density of water, $\rho=1000 kg/m^3$
Mass of the person, $M=\rho V$
$M=1000\times 0.12$
$M=120kg$
The correct option is C.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

FIll in the blank. 

When a solid floats in a liquid,  the weight of _______ by its immersed part of the solid is equal to the weight of the solid. 

  1. less

  2. buoyant force

  3. weight

  4. liquid displaced
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Liquid displaced.
This is known as Archimedes principle.
Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A cylinder is made up of a material of density $1.5\ g\ cm^{-3}$ is immersed inside a liquid of density $1\ g\ cm^{-3}$. State whether the cylinder moves up or not

  1. Yes

  2. No

  3. Maybe

  4. Can't say
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the volume of cylinder be V

So weight of cylinder is $W=V\rho _{cylinder}g=1.5Vg$
Buoyancy force $F=V\rho _{liquid}g=V\times 1\times g=Vg$
Since weight is greater than buoyancy, $W>F$, so it will move downward.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

$A$ and $B$ are two metallic pieces. They are fully immersed in water and then weighed. Now they show same loss of weight. The conclusion therefore is:

  1. $A$ and $B$ have same weight in air
  2. $A$ and $B$ have equal volumes
  3. The densities of the materials of $A$ and $B$ are the same
  4. $A$ and $B$ are immersed to the same depth inside water.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Same loss of weight implies equal buoyant forces on the object which is equal to weight of liquid displaced i.e. both the bodies have equal volumes.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

Two solids A and B Float is a liquid. It is observed that A floats with half its volume immersed and B floats with $2/3$ of its volume immersed. Compare the densities of A and B.

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

$\dfrac { density\quad of\quad A }{ density\quad of\quad B } =\dfrac { density\quad of\quad immersed }{ Volume\quad of\quad B\quad immersed } =\dfrac { 1/2 }{ 2/3 } $

$\dfrac { density\quad of\quad A }{ density\quad of\quad B } =\dfrac { 3 }{ 4 } $

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A piece of paraffin wax of density 0.9 g/cc floats on water.A layer of turpentine of density 0.87 g/cc is added on top of water until the wax is entirely submerged.The ratio of the volume of wax immersed in water to that in turpentine is 

  1. 3 : 13

  2. 87 : 90

  3. 90 : 87

  4. 3 : 10
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Buoyant force = weight of liquid displaced

hence $0.9V=1\times { V } _{ 1 }+0.87\times { V } _{ 2 }$
            & $V={ V } _{ 1 }+{ V } _{ 2 }$
               $0.9\left( { V } _{ 1 }+{ V } _{ 2 } \right) ={ V } _{ 1 }+0.87{ V } _{ 2 }$
               $0.9{ V } _{ 1 }+0.9{ V } _{ 2 }={ V } _{ 1 }+0.87{ V } _{ 2 }$
                        $\boxed { \dfrac { { V } _{ 1 } }{ { V } _{ 2 } } =\dfrac { 3 }{ 10 }  } $

Multiple choice physics forces in fluids experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

The densities of objects P,Q,R and S are ${200 kg/m^3}$, ${450 kg/m^3}$, ${1200 kg/m^3}$  and ${785 kg/m^3}$ respectively. Which one of these objects will sink when dipped in a bucket of water?

  1. P

  2. Q

  3. R

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

Answer is C.

According to the laws of flotation, the more denser liquid will sink below and the less dense material will float.
In this case, the object R has the maximum density of $1200kg/{ m }^{ 3 }$.
Therefore, object R will sink when dipped in a bucket of water.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A 70 g substance has a volume of $35:cm^3$. It will float on the surface of the water.

  1. True

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

Given:
Mass of substance $= 70g$.
Volume of substance $= 35cm^3$
density of water $= 1gm^{-3}$
By using the formula,
Density $=\dfrac{Mass}{Volume}$
Density of sub stance $= \dfrac{70}{35}=2gm^{-3}$
since, the density of the substance is more than the density, the gravitational force acting on it will be stronger than the buoyant force of water acting it, it will sink and not float on the surface of water

Multiple choice physics forces in fluids experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A piece of wood floats in water, completely inside it. What happens when it is dropped in ethanol?

  1. It floats higher

  2. Stays as before

  3. It sinks

  4. It sinks first and then rises
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since , the ethanol is less denser than the water.Therefore, a piece of wood floating completely in water will sink in the ethanol.

Multiple choice physics forces in fluids experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

As the density of a series of liquids increases, the upthrust on the iron rod submerged

  1. Increases

  2. Decreases

  3. Remains constant

  4. Noting can be said
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the density of liquid increases & so does the buoyant force on the submerged rod which will result in increase in upthrust.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

An object is placed in 3 beakers containing liquids A, B and C respectively. If the density of object (d) when compared to tensities of liquids A, B and C is given by $d _A < d < d _B < d _C$ then the body sinks in

  1. liquid A

  2. liquid B

  3. liquid C

  4. all the three liquids
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the density of the liquid is greater than that of object, then the weight of liquid displaced is greater than or equal to the weight of the object. This means that the buoyant force acting on the object is greater or equal to the weight of the object which makes the object to float in that liquid. 

Hence the object will float in liquids B and C as the densities of liquids B and C are more than that of the object while the object will sink in liquid A as the density of liquid A is less than that of the object.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications

A body of mass $120kg$ and density $600kg/{m}^{3}$ floats in water. What additional mass could be added to the body so that the body will just sink?

  1. $20kg$
  2. $80kg$
  3. $100kg$
  4. $120kg$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Weight of the water displaced= weight of body + additional mass

${ \rho  } _{ w }Vg=Mg$   ($M$ is the total mass)
${ \rho  } _{ w }V=M=\left( 100+m \right) \ V=\cfrac { 120 }{ 600 } =0.2{ m }^{ 3 }\ 1000\times 0.2=\left( 120+m \right) \ m=80kg$