Physics

Fluid Mechanics

673 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?

A wooden cylinder floats vertically in water with half of its length immersed, Density of wood is

  1. Equal to that of water

  2. Half the density of water

  3. Double the density of water

  4. One fourth the density of water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When an object floats with half of its volume immersed, the buoyant force equals its total weight. According to Archimedes' principle, the ratio of the immersed volume to total volume equals the ratio of the object's density to the fluid's density, making the wood's density half that of water.

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?

An object measuring $2\times 2\times 5{cm}^{3}$ has a mass of $16g$. It is put in water of density $1g/cc$. Percentage of its volume outside water while floating is

  1. $10$%
  2. $20$%
  3. $30$%
  4. $40$%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The volume of the object is 2 * 2 * 5 = 20 cm^3, and its mass is 16 g, giving a density of 16/20 = 0.8 g/cc. The fraction of volume submerged is equal to the relative density (0.8/1.0 = 0.8 or 80%), which means the percentage of volume outside water is 100% - 80% = 20%.

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?

A block of wood floats is water with $ 2/5^{th} $ of its volume above the surface Calculate the density of wood.

  1. $ 0.6 g/cm^3 $
  2. $ 1.6 g/cm^3 $
  3. $ 2.5 g/cm^3 $
  4. $ 3.6 g / cm^3 $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since 2/5th of the volume is above the surface, 3/5th of the volume must be immersed in water. The density of the wood is therefore 3/5 (or 60%) of the density of water, which equals 0.6 g/cm^3.

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 cubical box of wood of side $30\, cm$ weighing $21.6\, kg$ floats on water with two faces horizontal. The depth of immersion of box is :

  1. $30\, cm$
  2. $12\, cm$
  3. $6\, cm$
  4. $24\, cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For a floating body, the weight of the floating object equals the buoyant force, which is the weight of the displaced water. Using the dimensions of the cubical box, the mass divided by the area of the base gives the volume of water displaced per unit area, yielding the depth of immersion. Calculation: (21.6 kg) / (0.3 m * 0.3 m * 1000 kg/m^3) = 0.24 m or 24 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.

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?

The weight of the liquid displacement by a body when the body is immersed in it is called 

  1. Apparent weight

  2. Upthrust

  3. Lateral pressure

  4. Relative density of body
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Archimedes principle, when a body is immersed in a liquid, the upward buoyant force acting on it is equal to the weight of the liquid displaced by the body. This upward force is termed upthrust.

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?

Ice ______ in water, because the weight of water displaced by the immersed part of the ice is _____ its own weight 

  1. sinks, more than

  2. sinks, less than

  3. floats , equal to

  4. floats , less than
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Archimedes principle, A body immersed in water experiences an upward force equal to the mass of the fluid displaced by the body. If the weight of an object is greater than the weight of displaced fluid, it will float. If the two are equal, it is suspended, neither floating nor sinking. For example, when an object is placed in water, it will displace its own volume of water, and that water will push back against it proportionally, producing an upthrust.
Water has a weight density of $62$ pounds per cubic foot. It an object weighing $62$ pounds has a volume that displaces $2$ cubic feet of water, it will float. The displaced water will weigh $124$ pounds and the pressure of that water would be enough to keep the object floating.
Hence, Ice floats in water, because the weight of water is displaced by the immersed part of the ice is more than its own weight and the statement is true.