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 applications of floatation principle of floatation and its applications when do objects float on water?

An iceberg of density $900 kg/m3$ is floating in water of density $1000 kg/m3$. the percentage of volume of ice-cube outside the water is

  1. $10$ percent
  2. $20$ percent
  3. $31$ percent

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Let  V is the total volume of iceberg
       ${ V } _{ sub }$ = volume of iceberg submerged
        ${ \rho  } _{ b }$= density of iceberg = 900 Kg/m3
         ${ \rho  } _{ w }$= density of water = 1000 Kg/m3
 So, for the flotation of body,
             weight of body= weight of water displaced
           $\Rightarrow{ \rho  } _{ b }V={ \rho  } _{ w }{ V } _{ sub }$
           $\Rightarrow \dfrac { { V } _{ sub } }{ V } =\dfrac { { \rho  } _{ b } }{ { \rho  } _{ w } } $
substracting both side from 1, we get
             $\Rightarrow 1-\dfrac { { V } _{ sub } }{ V } =1-\dfrac { { \rho  } _{ b } }{ { \rho  } _{ w } } $
            $\Rightarrow \dfrac { V-{ V } _{ sub } }{ V } =\dfrac { { \rho  } _{ w }-{ \rho  } _{ b } }{ { \rho  } _{ w } } $
             Converting it in percentage,
              $\Rightarrow \dfrac { V-{ V } _{ sub } }{ V } \times 100=\dfrac { { \rho  } _{ w }-{ \rho  } _{ b } }{ { \rho  } _{ w } } \times 100$
by  substituting values, we get
            percentage volume outside the water= $\dfrac { 1000-900 }{ 1000 } \times 100=10$%

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A wooden cube floats in water partially immersed. When 200 g weight is put on the cube, it further immersed by 2 cm. The length of the side of the cube is

  1. $1.0 cm$
  2. $\sqrt{10}cm$
  3. $10 cm$
  4. $20 cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The additional weight of 200g causes an additional displacement of water equal to the volume of the cube submerged by 2cm. Thus, 200g = (Area * 2cm) * density_water. Solving for the side length L where Area = L^2 gives 10cm.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A ball weighing  $4 kg$  of density  $4000{ kg }\quad { m }^{ { -3 } }$  is completely immersed in water of density  $1000{ kg }\quad { m }^{ { -3 } }.$  Find the force of buoyancy on it. (Given $g = 10 { ms } ^ { - 2 }$)

  1. $100{ N }$
  2. $1{ N }$
  3. $20{ N }$
  4. $10{ N }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Buoyant force is equal to the weight of the displaced liquid. Volume of the ball = mass / density = 4kg / 4000kg/m^3 = 0.001 m^3. Buoyant force = volume * density_water * g = 0.001 * 1000 * 10 = 10 N.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A block of wood is floating in water in a closed vessel as shown in the figure. The vessel is connected to an air pump. When more air is pushed into the vessel, the block of wood floats with : (neglect compressibility of water)

  1. Larger part in the water

  2. Smaller part in the water

  3. Same part in the water

  4. At some instant it will sink
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The buoyant force depends on the weight of the displaced fluid. Since the block is floating, the buoyant force equals the weight of the block. Increasing air pressure does not change the density of the water or the weight of the block, so the submerged volume remains the same.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

We have two different liquids A and B whose relative densities are 0.75 and 1.0, respectively. If we dip solid objects P and Q having relative densities 0.6 and 0.9 in these liquids, then:

  1. P floats in A and Q sinks in B

  2. P sinks in A and Q floats in B

  3. P floats in B and Q sinks in A

  4. P sinks in B and Q floats in A
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If solid object has higher density than liquid then it will sink in that liquid otherwise it will float.
R.D. of liquid A = 0.75
R.D. of liquid B = 1.0
R.D. of object P = 0.6
R.D. of object Q = 0.9

  • P has R.D. less then both the liquids. so it will float in both the liquids.
  • Q has R.D. more than liquid A, so it will sink in A.
  • Q has R.D. less than liquid B, so it will float in B.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A cube of wood supporting a $200$ gm mass just floats in water. When the mass is removed the cube rises $2$ cm at equilibrium. Find size of the cube.

  1. 10cm

  2. 12cm

  3. 15cm

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

The weight of the 200g mass equals the weight of the water displaced by the additional 2cm immersion. 200g = (Area * 2cm) * density_water. Area = 100 cm^2. Side length = 10 cm.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A hollow cylinder of copper of length $25\, cm$ and area of cross-section $15\, cm^2$, floats in water with $3/5$ of its length inside water. Then 

  1. Apparent density of hollow copper cylinder is $0.6\, gcm^{-3}$
  2. Weight of the cylinder is $225\, gf$
  3. Extra force required to completely submerge it in water is $150\, gf$
  4. Extra force required to completely submerge it in water is $225\, gf$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Weight of the cylinder = buoyant force = (3/5 * 25 cm * 15 cm^2) * 1 g/cm^3 = 225 gf. This confirms option B.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

Two solids $A$ and $B$ float in water. It is observed that $A$ floats with half its volume immersed and $B$ floats with $\dfrac{2}{3}$ 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

For a floating object, density_object / density_fluid = fraction_submerged. Density_A / Density_water = 1/2. Density_B / Density_water = 2/3. Ratio A:B = (1/2) / (2/3) = 3/4.