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 physics forces and matter pressure in fluids pressure in liquids introduction to pressure

Calculate the pressure exerted by water at the bottom of a lake of depth 6 m. (Density of water $=1000 kg m^{-3}, g=10 ms^{-2})$.

  1. $2\times 10^4 Pa$
  2. $4\times 10^4 Pa$
  3. $6\times 10^4 Pa$
  4. $8\times 10^4 Pa$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Height $(h)=6 m$,

$density=1000 kg m^{-3}$,
$g=10 m s^{-2}, Pressure = ?$
$P=hdg$
$=6\times 1000\times 10 Pa$
$=60000 Pa$
$=6\times 10^4 Pa.$

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

Calculate the vertical height of a mercury column which exerts a pressure of 81600 Pa. (Density of mercury is $13.6 g cm^{-3}$ and $g=10 ms^{-2})$.

  1. 0.2 m

  2. 0.4 m

  3. 0.6 m

  4. 0.8 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$Pressure (P)=81600 Pa$
$Density (d)=13.6 g cm^{-3}$
$=13.6\times 1000 kg m^{-3}$
$(\therefore 1 g cm^{-3}=1000 kg m^{-3})$

Acceleration due to gravity $(g)=10 ms^{-2}$
$P=hdg$
$\Rightarrow h=\dfrac {P}{dg}=\dfrac {81600}{13.6\times 1000\times 10}$
$\Rightarrow h=0.6 m$
Therefore, vertical height of mercury column is 0.6 m.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

A liquid of density $12 kg m^{-3}$ exerts a pressure of 600 Pa at a point inside a liquid. What is height of liquid column above that point? $[g=10 ms^{-2}]$

  1. 4 m

  2. 5 m

  3. 6 m

  4. 7 m
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$Denstiy = 12 kg m^{-3}, Pressure=600 Pa$
$Pressure=hdg$
$\Rightarrow hdg=Pressure\Rightarrow height=\dfrac {P}{dg}$
$=\dfrac {600}{12\times 10}m=5m.$

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

A metal cube is placed in an empty vessel. When water is filled in the vessel so that  cube is completely immersed in the water, the force on the bottom of the vessel in contact with the cube-

  1. Will increase

  2. Will decrease

  3. Will remain the same

  4. Will become zero
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Archimedes' principle, the buoyant force acting on the cube is equal to the weight of the water displaced. Since the cube is resting on the bottom, the total downward force exerted on the bottom of the vessel remains the same because the weight of the water added is balanced by the buoyant force pushing up on the cube.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

Two stretched membranes of area $2 cm^2$ and $3 cm^2$ are placed in a liquid at the same depth. The ratio of the pressure on them is :

  1. $1 : 1$
  2. $2 : 3$
  3. $3 : 2$
  4. $2^2 : 3^2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

pressure depends on depth not on area so the two stretched membrane would  have  equal pressure.

so ratio of their pressures would be 1 : 1.
hence option (A) is correct

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

Fill in the blank

Fluids at a given depth exert ______ pressure in all directions 

  1. same

  2. independent

  3. different

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

Fluids at a given depth exert same pressure in all directions.
Pressure of a liquid is directly proportional to the depth, and for a given depth the liquid exerts the same pressure in all directions according to Pascal's law.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

A block of wood floats separately in river water and then in ocean water. Then the weight of the displaced river water is

  1. equal to the weight of the displaced ocean water.

  2. less than the weight of the displaced ocean water.

  3. more than the weight of the displaced ocean water.

  4. not dependent on the density of the wooden block.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to the law of flotation, a floating object displaces a weight of fluid equal to its own weight. Since the weight of the wooden block is constant regardless of the fluid it floats in, the weight of the displaced fluid must be the same in both river water and ocean water.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

There are two fish tanks each of depth $0.5 m$. Base area of one is $0.5m^2$ and that of another is $0.1m^2$. At the depth of which tank will a fish feel larger pressure?

  1. The tank of wider base area

  2. The tank of smaller base area

  3. Equal for both tanks

  4. Can't say
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Liquid pressure is given by =$ \rho \times g \times h$
Liquid pressure depends on the depth and not on surface area. Both the tanks have the same depth. So, for both the tanks, the fish will feel equal pressure.

Multiple choice physics forces and matter pressure in fluids pressure in liquids introduction to pressure

The size of an air bubble rising up in water.

  1. Decreases

  2. Increases

  3. Remains same

  4. May increase or decrease
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 As the pressure exerted by water is directly proportional to the depth of water, as the depth of water increases in a water body, the pressure increases linearly. So when a air bubble rises in water, the pressure acting on the air bubble decreases. 


We know the that as the the pressure acting on gas is inversely proportional to the volume occupied by it i.e. if the pressure increases, then the volume occupied will decrease and if the pressure acting on the gas decreases, then the volume occupied by by the gas will increase.


In the rising air bubble, as the pressure is decreasing, the volume and hence its size increases.

so option (B) is correct.