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

It is said that there is a vacuum in a vessel when

  1. air is completely filled in the vessel

  2. air is partially removed from the vessel

  3. air is completely removed from the vessel

  4. water is completely removed from the vessel
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When air is completely removed from a vessel, it is said that there is vacuum in the vessel.

Multiple choice

A fresh egg sinks in pure water where as it floats in salty water

  1. Due to higher density of salty water

  2. Due to higher density of pure water

  3. Due to fluid matter inside the egg shell

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

Salt water has higher density than pure water. The egg's density is between the two - it sinks in less dense pure water but floats in denser salt water due to buoyancy.

Multiple choice

Rain drop is always spherical in shape because

  1. liquid tends to possess minimum surface tension area

  2. liquid tends to possess maximum surface tension area

  3. liquid tends to possess zero surface tension area

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The shape of a drop of rain is constrained by the surface tension, which tries to give it the shape for which the surface area is minimum. For a given volume, the spherical shape has the minimum surface area. That is why rain drops acquire spherical shape.

Multiple choice

Which of the following statements is/are false? a. The high air pressure produced by the gas molecules on the walls of baloon causes it to expand and get inflated. b. The pressure exerted by a liquid on the walls of its container increases with the increasing depth. c. The rise of liquid in a dropper is due to the gravitational force.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Statement 'c' is a false statement. Thus, it is the correct option. The rise of liquid in a dropper is due to the atmospheric pressure.

Multiple choice

Which of the following statements is/are false? a. The pressure exerted by a liquid decreases with the increase in depth inside the liquid. b. The same force produces less pressure if it acts on a large area but it can produce high pressure if it acts on a smaller area. c. The SI unit of pressure is pascal.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Statement 'a' is a false statement. Thus, it is the correct option. The pressure exerted by a liquid increases with the increase in depth inside the liquid.

Multiple choice

Small drops of water are spherical in shape because of

  1. gravitational force

  2. adhesion

  3. surface tension

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

Surface tension is the cohesive force between liquid molecules that causes water droplets to minimize their surface area. A sphere has the minimum surface area for a given volume, which is why small water droplets naturally form spherical shapes.

Multiple choice

Bar is a unit of

  1. atmospheric pressure

  2. water pressure

  3. buoyant force

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Bar is a metric unit of pressure equal to 100,000 Pa (pascals). It is commonly used to express atmospheric pressure, where 1 bar is approximately equal to Earth's atmospheric pressure at sea level. It is not specifically for water pressure or buoyant force, though it can measure any pressure.

Multiple choice

A falling drop of water acquires spherical shape due to

  1. atmospheric pressure

  2. gravitational force

  3. surface tension

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

Surface tension minimizes the surface area of a liquid for a given volume, causing water droplets to become spherical (a sphere has minimum surface area). Atmospheric pressure and gravitational force act externally, while 'capillary rice' is a typo for 'capillary rise' (a different phenomenon).

Multiple choice

Water has highest density at

  1. 00 C

  2. 40 C

  3. 1000 C

  4. 100 C
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Water reaches its maximum density at approximately 4°C (39°F). This unusual property occurs because water molecules form a highly ordered structure as temperature decreases from 4°C to 0°C, causing expansion. This property is crucial for aquatic life as ice floats, insulating the water below and allowing organisms to survive under frozen surfaces.

Multiple choice

Riya poured water in the glass and put some ice in it. She noticed that the ice was floating in the glass. Which of the following is the correct reason as to why ice floats on water?

  1. Surface tension of water is more than that of ice.

  2. Density of water is more than ice.

  3. Mass of ice is more than that of water.

  4. Density of ice is more than that of water.

  5. Surface tension of ice is more than that of water.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is the correct option. Ice floats because it is about 9% less dense than liquid water. In other words, ice takes up about 9% more space than water. The heavier water displaces the lighter ice, so ice floats to the top.  

Multiple choice

Consider the following statements:The fraction of a ball floating inside the liquid depends upon

  1. density of the liquid
  2. mass of the ball
  3. density of the ball Which of the statements given above are correct?

  1. 1 and 2 only

  2. 2 and 3 only

  3. 1 and 3 only

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

According to Archimedes' principle, the fraction of a floating object submerged depends on the ratio of the object's density to the liquid's density. The mass of the ball is irrelevant - only the densities matter. For a given liquid density, balls with the same density will float at the same level regardless of mass.

Multiple choice

A jug of water when fully immersed in a bucket of water does not feel as heavy as when it is taken completely out of water. This can be explained on the basis of

  1. capillary action of water

  2. Pascal's law

  3. Archimedes principle

  4. surface tension of water
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Archimedes' principle, an object immersed in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid. When the jug is in the bucket of water, the buoyant force reduces its apparent weight. When removed from water, this force disappears and the full weight is felt.

Multiple choice

The fraction of the total volume of an iceberg of density 0.93 floating in North Sea with density of 1.03 gm/cm3 is

  1. 1%

  2. 11%

  3. 21%

  4. 75%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a floating body, the fraction submerged equals the ratio of densities: fraction_submerged = density_iceberg / density_water. Here: 0.93/1.03 = 0.9029, meaning about 90.29% is submerged. The visible (above water) fraction is 1 - 0.9029 = 0.0971 or 9.71%, which rounds to approximately 11%. Option B is closest.