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 general knowledge science & technology

An astronaut on earth notes that in her soft drink an ice cube floats with 9/10 its volume submerged. If she were instead in a lunar module parked on the moon, the ice in the same soft drink would float with

  1. less than 9/10 submerged.

  2. 9/10 submerged.

  3. more than 9/10 submerged.

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

The fraction of an ice cube submerged depends only on the density ratio of ice to liquid, not on gravitational acceleration. This ratio is unchanged on the moon, so the submerged volume remains 9/10.

Multiple choice general knowledge

Siphon will fail to work if

  1. the densities of the liquid in the two vessels are equal

  2. the level of the liquid in the two vessels are at the same height

  3. both its limbs are of unequal length

  4. the temperature of the liquids in the two vessels are the same
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A siphon works due to gravitational pressure difference, with liquid flowing from the higher vessel to the lower one. If both liquid levels are at the same height, there's no pressure difference to drive the flow. Equal density, unequal limb length, or equal temperature don't prevent siphon action - it's the equal height that eliminates the driving force.

Multiple choice general knowledge science & technology

Siphon will fail to work if

  1. the densities of the liquid in the two vessels are equal

  2. the level of the liquid in the two vessels are at the same height

  3. both its limbs are of unequal length

  4. the temperature of the liquids in the two vessels are the same
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A siphon operates due to the pressure difference created by a height difference between liquid levels. When both vessels have liquid at the same level, there's no gravitational pressure gradient to drive flow, causing the siphon to fail regardless of tube configuration.

Multiple choice general knowledge

The tendency of a liquid drop to assume spherical shape is due to what

  1. surface tension

  2. viscosity

  3. density

  4. kinematic viscosity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Surface tension is the cohesive force that causes liquid droplets to minimize their surface area by assuming a spherical shape. Among the options, surface tension is the correct physical phenomenon responsible for this behavior. Viscosity relates to fluid flow resistance, density to mass per volume, and kinematic viscosity to viscosity divided by density.

Multiple choice

Why does needle float, when it is placed horizontally on the surface of water?

  1. Viscosity of water

  2. Capilary action

  3. Water pressure

  4. Surface tension of water

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

Surface tension of water is a contractive tendency of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects (e.g water striders to run on the water surface. This property is caused by cohesion of similar molecules and is responsible for many of the behaviors of liquids..

Multiple choice

Why does a drop of liquid assume spherical shape?

  1. Intermolecular forces are weak in liquids.

  2. Intermolecular forces are strong in liquids.

  3. A sphere has the no surface area for a given volume.

  4. A sphere drop acts inwards to the center so drop tends to reduced its volume.

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The surface tension of liquid is responsible for that ,the tension at surfaces of a drop acts inwards to the center so drop tends to reduced its volume and the minimum possible volume for matter is a sphere and therefore a falling drop of liquid acquires the spherical shape.

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

At its deepest, the lake is

Directions: Read the following passage and answer the question that follows.

Lost Lake that lies in Oregon's Mount Hood National Forest is a mysterious natural wonder. During winters, it resembles any other large body of fresh water. However, as drier weather kicks in, the water disappears, transforming the 85 acre 'lake' into a beautiful meadow. It turns out that there is a logical answer to this magical phenomenon - a tube or tunnel created by an ancient lava flow that drains out the water.
Jude McHugh, a spokeswoman for the Willamette National Forest in Oregon, says that the lakebed starts to fill during the rainy season in the fall. As the lava tube measures just six-feet in diameter, it is unable to drain the water fast enough. As a result, the lake, which is 167 ft at its deepest, manages to remain full, despite the fact that some water is always seeping out. This continues through spring as the snow from the surrounding mountains melts. But once the steady flow of water stops, the constant drainage causes the lake to "disappear".

  1. 167 ft

  2. 85 acres

  3. 120 metres
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The line 'As a result, the lake which is 167-ft at its deepest, manages to remain full...' suggests the answer.

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.