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 archimedes' principle fluid pressure properties of matter physics

A slid floats in a liquid in a partially dipped position.

  1. The solid exerts a force equal to its weight on the liquid

  2. The weight of the displaced liquid equals the weight of the solid

  3. The liquid exerts a force of buoyancy on the solid which is equal to the weight of the solid

  4. The weight of the dipped part of the solid is equal to the weight of the displaced liquid
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

The force that solid exerts on liquid is its weight. Hence option A is correct.
Since the solid is stationary, the weight of solid is equal to the force exerted on it by liquid.
According to Archimedes' Principle, the buoyant force acting upwards on the solid is equal to the weight of the liquid displaced. Hence option B and C are correct.

Multiple choice archimedes' principle fluid pressure properties of matter physics

When a body is wholly or partly immersed in a liquid it experiences. 

  1. An up-thrust or down-thrust depending on the density of the liquid

  2. An up-thrust

  3. A down-thrust

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

Whenever a body is wholly or partially immersed in a liquid it experience an upthrust or buoyant force.

Multiple choice archimedes' principle fluid pressure properties of matter physics

The principle on which Hare's apparatus works on is.

  1. Bernoulli's principle

  2. Archimedes principle

  3. Newton's law

  4. Kepler's law
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hare`s apparatus is used  to compare the densities of two liquids and is base on Archimedes principle .

so option (B) is correct

Multiple choice archimedes' principle fluid pressure properties of matter physics

The upward thrust exerted on the body by the liquid acts vertically upwards through the center of gravity of the displaced liquid.

  1. True

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

when a body is immersed in a fluid an downward force mg acts on it and to balance this force an upward force kown by the name buoyant force is exerted by the fluid .

so given statement is true , hence option ( A) is correct

Multiple choice archimedes' principle fluid pressure properties of matter physics

A body is floating in a given liquid with half of its volume above the surface of the given liquid. If the body is slightly pushed into the liquid, then the body,

  1. sinks in the liquid and settles at the bottom.

  2. come back to its position after some time.

  3. keeps oscillating in vertical direction.

  4. it jumps into the air and falls on the liquid.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Before pushing body was in the position of equilibrium so if we disturbs the eqm than with the passage of time it would come back to its eqm position .

so option (B) is correct

Multiple choice archimedes' principle fluid pressure properties of matter physics

Apparent loss of weight of a body when immersed in a liquid can be explained on the basis of 

  1. molecular theory.

  2. electron theory.

  3. Archimedes' principle.

  4. Bernoulli's principle.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Archimedes principle states that  loss in weight of a partially or fully immersed body in a fluid is equal to the weight of the fluid displaced .

so , option (C) is correct

Multiple choice archimedes' principle fluid pressure properties of matter physics

A ball floats on the surface of water in a container exposed to the atmosphere. Will the ball remain immersed at its former depth or will it sink or rise if the container is covered and the air is removed:

  1. The ball sinks

  2. The ball rises

  3. The ball remains immersed at its former depth

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

The ball floats due to the buoyant force, which depends on the pressure gradient in the fluid. When the air is removed, the pressure at the surface becomes zero, but the pressure gradient (rho*g*h) remains the same as long as the fluid is incompressible; however, if the ball is held up by air pressure or if the surface tension/meniscus changes, it might sink. In standard physics problems of this type, the removal of atmospheric pressure does not change the buoyancy of a submerged object, but if the ball is floating, the lack of air pressure on the top surface while the water pressure remains below causes it to sink deeper.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A wooden block is taken to the bottom of a lake of water and then released . it rise up with a 

  1. Constant acceleration

  2. Decreasing acceleration

  3. Constant velocity

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

As the wooden block rises, the buoyant force remains constant (rho*V*g) while the weight is constant. Since the density of wood is less than water, the net upward force is constant, resulting in constant acceleration.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A cube of wood supporting $200 \mathrm { gm }$ mass just floats in water in fully submerged state. When the mass is removed cube rises by $2 \mathrm { cm }$ above water level. Find the size of cube? (take $\rho _ { \text { water } } = 1000 \mathrm { kg } / \mathrm { m } ^ { 3 } )$

  1. $10 \mathrm { cm }$
  2. $15 \mathrm { cm }$
  3. $20 \mathrm { cm }$
  4. $30 \mathrm { cm }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the 200 gm mass is removed, the buoyant force decreases by an amount equal to the weight of 200 gm, which corresponds to the volume of the cube of side L that rises by 2 cm (h = 2 cm). Thus, buoyant force difference = A * h * rho_w * g = 200 gm * g. Solving L * L * 2 cm * (1 g/cm^3) = 200 g gives L^2 = 100 cm^2, so L = 10 cm.

Multiple choice archimedes' principle fluid pressure properties of matter physics

A boat full of scrap iron is floating on water in a lake. If all the iron is dropped into the water, the level of water will:

  1. go up

  2. fall down

  3. remain the same

  4. Can not be decided.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
According to Archimedes' principle, any body completely or partially submerged in a fluid at rest is acted upon by an upward, or buoyant force,the magnitude of which is equal to the weight of the fluid displaced by the body
As boat filled with scrap iron is floating on lake, buoyant force acting on boat is more than its weight.
                                              $F _b > W _b + W _{fe}$
since,                                    $W _b<W _b +W _{fe}$
therefore,level of water will fall down across the boat.
Multiple choice archimedes' principle fluid pressure properties of matter physics

If a piece of wood just floats in water. What happens to it in ethanol?

  1. It floats higher

  2. It stays as before

  3. It sinks

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

At room temperature and standard pressure, the first family of alcohol (methanol, ETHANOL and iso-propyl) all have densities of about 0.79g/cc compare to water at the same conditions with a density of 1.0g/cc.

Since the density of ethanol is less than the density of water so, when a piece of wood which is just floating in water is placed in ethanol, sinks.

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