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 archimedes' principle fluid pressure properties of matter physics

A boat is floating on the surface of water in a tank carrying steel balls. If the balls are thrown into the tank one by one, how will it affect the level of water?

  1. It will rise

  2. It will fall

  3. It will remain unchanged

  4. First it will rise and then fall
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the balls are in the boat, they displace water equal to their weight. When thrown into the tank, they displace water equal to their volume. Since the density of steel is much greater than water, the volume of water displaced when submerged is less than the volume of water displaced when floating, causing the water level to fall.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A dog is sitting in a boat which is floating in a pond. If the dog drinks some water from the pond then:

  1. the level of water in the pond decreases

  2. the level of water in the pond increases

  3. the level of water in the pond first increases, then decreases

  4. the level of water in the pond remains unchanged
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

There Will be no change in the water level of the pond, as the water which was drawn from the pond went to the man's body, thereby increasing his weight. So the decrease in level of water will be compensated by volume displaced by increase in weight of the man.

Therefore option $D$ is correct.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A vessel completely filled with water is weighed. This vessel will weigh ________ after a wooden block is gently moved into the water until it stays in equilibrium while any displaced water is removed.

  1. More

  2. Same

  3. Less

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

False because the liquid displaced has the same weight as the wooden block has The weight of the displaced liquid from the vessel is same as the weight of the wooden block.
Hence,  the weight will remain the same.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A sphere is floating in water its $\dfrac{1}3rd$ part is outside the water and when the sphere is floating in unknown liquid, it's $\dfrac {3}{4}th$ part is outside the liquid than the density of the liquid is

  1. $\dfrac{4}9\ gm/cc$
  2. $\dfrac{9}4\ gm/cc$
  3. $\dfrac{8}3\ gm/cc$
  4. $\dfrac{3}8\ gm/cc$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

volume of liquid inside the liquid1=2/3rd of total volume

volume of liquid inside the liquid2 = 1/4th of total volume

density of liquid= (2/3)/(1/4) = 8/3 g/cc

Multiple choice archimedes' principle fluid pressure properties of matter physics

A boat carrying steel balls is floating on the surface of water in a tank.If the balls are thrown into the tank one by one , how will it affect the level of water :

  1. It will remain unchanged

  2. It will rise

  3. It will fall

  4. First it will raise and then fall
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since the weight remains constant & so does buoyant force on a floating body. Hence there will be no change in level of water.

Multiple choice archimedes' principle fluid pressure properties of matter physics

Choose the correct statement from the following:

  1. A body will sink in a liquid if its weight is equal to or greater than the weight of the liquid displaced by it

  2. A body will float in a liquid if its weight is equal to or less then the weight of liquid displaced by it

  3. When a body floats in a liquid, the portion of the body above the surface of the liquid is independent of the density of the body relative to that of the liquid

  4. In still air, a hydrogen filled balloon rises up to certain height and then stops rising.
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation
According to Archimedes
${ F } _{ b }=$weight of liquid displaced by object
The object floats if ${ F } _{ b }\ge mg$
Weight of liquid displace$\ge $ weight of object
When a body floats the portion immersed or above liquid is dependent on body's density.
The balloon rises till ${ F } _{ b }> mg$. Then stops, since ${ F } _{ b }$ decreases as air gets thin.
Multiple choice evs look, learn and experience brief introduction to atoms of elements elements and atoms introduction of atom

As a balloon is filled with water,it expands and increases in weight,This shows that water:

  1. Has mass

  2. Occupies space

  3. Is a kind of matter

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The balloon expands shows that the water n the balloon is occupying the space and the increase in weight of the balloon proves that water has mass and Matter is anything that has mass and takes up space.

Multiple choice physics isothermal and adiabatic processes work done by an ideal gas in isothermal expansion thermodynamic processes heat and thermodynamics

Two soap bubbles having radii $3\ cm$ and $4\ cm$ in vacuum, coalesce under isothermal conditions. The radius of the new bubble is

  1. $1\ cm$
  2. $5\ cm$
  3. $7\ cm$
  4. $3.5\ cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For soap bubbles coalescing isothermally, the total number of moles of air remains constant. Using PV = nRT, and P = 4T/R (where T is surface tension), the pressure-volume product is proportional to R^2. Since (4T/R1)*V1 + (4T/R2)*V2 = (4T/R_new)*V_new, and V is proportional to R^3, we get R1^2 + R2^2 = R_new^2.

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

Which one of the following statements is true?

  1. Archimedes' principle can also be applied to gases

  2. The buoyant force depends on the nature of object immersed in the liquid.

  3. Ice floats in water because the density of ice is more than that of water.

  4. Force acting on a unit area is called thrust.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

The Archimedes principle, states that the buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid the body displaces. In other words, to calculate the buoyant force on an object we assume that the submersed part of the object is made of water and then calculate the weight of that water.
This principle is valid for any fluid not only liquids (such as water) but also gases (such as air).

 
Hence, only the statement in option A is true.

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

An iron needle sinks in water as its density is less than 1 $ \displaystyle g/cm^{3} $.

  1. True

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

Any substance sinks in a liquid of density of S when density of substance is greater than that of liquid i.e.

$\boxed { density\quad of\quad substance\quad >\quad S } $

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

If a body X floats in liquid Y. The density of body X is greater than liquid Y. True or false

  1. True

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

For a body to sink in water then density of body should be more than density of water or any fluid i.e. density of body > density of water.

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

Archimedes' principle states that the buoyant force applied to an object 

  1. is greater the weight of the fluid the object displaces

  2. is equal to the weight of the fluid the object displaces

  3. is less than the weight of the fluid the object displaces

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

Archimedes' principle states that the buoyant force applied to an object is equal to the weight of the fluid the object displaces.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications
Archimedes principle works when the body is

  1. Partially immersed in a liquid

  2. Fully immersed in a liquid

  3. Both A and B

  4. This principle has nothing to do with the level of immersion of the body
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Archimedes' Principle states that buoyant force acting on body upwards is equal in magnitude of the weight of liquid it displaces. Depending upon how much the body is immersed in liquid, and hence how much the weight of liquid is displaced, the buoyant force varies.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation experimental verification of archimedes' principle archimedes' principle archimedes' principle and its applications
When an object is immersed in water, it displaces $20\,kg$ of water. How much is the buoyant force acting on the object in Newtons?
  1. $100$
  2. $200$
  3. $0$
  4. $400$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the Archimedes principle, the buoyant force acting on an object immersed in liquid is equal to the weight of liquid it displaces. Hence the buoyant force acting on the given object=$20kg\times 10m/s^2=200N$

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. 

As per Archimedes principle the buoyant force on a submerged object is equal to_______ of liquid displaced by object. 

  1. Height

  2. Weight

  3. Nature

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

According to the Archimedes principle, the buoyant force of a submerged object is equal to the weight of the liquid displaced.

$\therefore$ Buoyant force     $B = \rho gV$    where $\rho$ and $V$ is the density of liquid and volume of object respectively.