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

Liquid drops and bubbles acquire spherical shape due to the phenomenon of ______.

  1. capillary

  2. surface tension

  3. gravitational effect

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

Surface tension is the property of liquid surfaces to shrink to the minimum possible area. For a given volume, the shape with minimum surface area is a sphere. This is why liquid drops and bubbles naturally acquire spherical shapes - surface tension minimizes the surface area.

Multiple choice

Manohar threw a stone in a pond and the stone sunk in the water. Why?

  1. The force exerted by the stone is greater than buoyancy of fluid.

  2. The force exerted by the stone is equal to the buoyancy of the fluid.

  3. There is no upward force exerted by the water.

  4. There is only gravitational force acting on it.

  5. The density of the stone is less than the density of the fluid.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Yes, if the force exerted by the object is greater than the upward thrust or buoyancy by water, the object sinks in water otherwise it floats over water.

Multiple choice

Which of the following statements is false regarding buoyancy?

  1. It is the upward force exerted by all the objects.

  2. If the density of the object is greater than the density of the fluid, the weight will be more than the buoyancy.

  3. If the object is floating on water, it has positive buoyancy.

  4. Because of buoyancy of air a bird or aeroplane can fly in air.

  5. Buoyancy is affected by the volume of the immersed object.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Yes, it is the correct answer, as this is the false statement regarding buoyancy. Buoyancy is the upward force exerted by fluids over the surface area of contact of an object which is immersed in fluids.

Multiple choice

A diver is able to cut through water in a swimming pool because

  1. water particles are very small

  2. water particles have high potential energy

  3. the force of attraction among the particles of water is less

  4. water particles have high kinetic energy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A diver is able to cut through water in a swimming pool because the force of attraction among the particles is less. If the force had been strong, the diver would not have been able to cut that force. Moreover, the particles of water are continuously moving with some kinetic energy (although the magnitude of kinetic energy is not very high). They don’t possess potential energy.

Multiple choice

According to the principle of flotation

  1. weight of the liquid displaced > weight of the floating body

  2. weight of the liquid displaced < weight of the floating body

  3. weight of the liquid displaced = weight of the floating body

  4. independance on the weight of the body

  5. liquids
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to the principle of flotation, weight of the liquid displaced is equal to the weight of the floating body.

Multiple choice

Consider the following statements:1. In a beaker, a plank of wood floats in water. If the beaker moves with a vertical acceleration, the wooden plank will sink deeper into the liquid.

  1. An ice cube containing a lead piece in it is floating in a glass of water. As ice melts, the water level will fall.

Which of the given statements is/are correct?

  1. Only (1)

  2. Only (2)

  3. Both (1) & (2)

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

Statement (1) is wrong. If the beaker moves with a vertical acceleration, the wooden plank will remain in the same position relative to the water.

Statement (2) is correct. The lead piece has greater density, while the ice cube is floating, it will be displacing a volume of water equal to the weight of the ice plus the weight of the iron. When the ice has melted, the iron will sink. Its volume will displace the same volume of water, its weight no longer has a bearing on how much is displaced.
Multiple choice

For a liquid surface:

  1. Surface stress = specific surface energy

  2. Surface stress > Specific surface energy

  3. Surface stress < specific surface energy

  4. There is no relation between surface stress and surface energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This option is correct because for liquids there is no strain tensor and surface stress is equal to specific surface energy. Indeed, if one tries to increase the surface area of a liquid, the bulk atoms will move to the surface to keep the density constant.

Multiple choice

If we put puffed puri in a bowl full of water

  1. it will sink

  2. it will float

  3. it will remain unaffected

  4. it will partially float and partially sink
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The puffed puri is filled with air and it is lighter than water so it will float.