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

A tank filled with water is placed in vacuum. The net pressure at point which is $10 m$ below the surface of water will be $(g = 10 m/s^2)$

  1. $100 \ kPa$
  2. $10 \ kPa$
  3. $1 \ kPa$

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

In a vacuum, there is no atmospheric pressure acting on the surface of the water. The pressure at a depth h is given by P = rho * g * h. Here, rho = 1000 kg/m^3, g = 10 m/s^2, and h = 10 m, so P = 1000 * 10 * 10 = 100,000 Pa = 100 kPa.

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.

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

Liquid rise in a syringe when its piston is pulled up due to 

  1. Atmospheric pressure

  2. Inertia of motion

  3. Inertia of rest

  4. Conservation of momentum
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the piston is pulled up, air pressure inside syringe reduces because of increase in volume. While pressure outside syringe is more than that. So, it pushes liquid into syringe.

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

What is the relationship between liquid pressure and the depth of a liquid?

  1. Directly proportional

  2. Inversely proportional

  3. Linear

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

The relationship between liquid pressure and the depth of a liquid:

Pressure at depth 'h' = density of fluid $\times $ acceleration due to gravity 'g' $\times $  depth 'h'.
Pressure is directly proportional to depth. If we triple the depth, we triple the pressure.

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

The pressure a liquids exerts against the sides and bottom of a container depends on the 

  1. atmospheric pressure

  2. surface area

  3. volume of container

  4. density and depth of liquid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\because p = h\times d\times g$
where, p = pressure, h = depth (height), d = density,  g = acceleration due to gravity = constant.

So, pressure depends on density and depth of liquid.

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

A tank $5\ m$ high is half filled with water and then is filled to the top with oil of density $0.85\ g\ cm^{-3}$. The pressure at the bottom of the tank, due to these liquids, is

  1. $1.85\ g$
  2. $89.25\ g\ dyne\ cm^{-3}$
  3. $462.5\ g\ dyne\ cm^{-2}$
  4. $500\ g\ dyne\ cm^{-2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We know that the pressure increases as we go deep into a liquid. The relation is given by $\Delta P = \rho g\Delta h$


Given that the tank is half filled with water and half with oil.
Thus, $h _\textrm{oil} = 2.5\textrm{ m}$ and $h _\textrm{water} = 2.5\textrm{ m}$

Thus, pressure at the bottom of the tank is $\Delta P = \Delta P _\textrm{oil} + \Delta P _\textrm{water} = 0.85\times 250g + 1\times 250g=462.5g \textrm{ dyne cm}^{-2}$