Mechanical Properties of Fluids Questions and Answers AP Inter 1st Year Physics Chapter 9

Andhra Pradesh BIEAP AP Inter 1st Year Physics Study Material 9th Lesson Mechanical Properties of Fluids Class 11 Textbook Exercise Questions and Answers.

Mechanical Properties of Fluids Class 11 Questions and Answers AP Inter 1st Year Physics 9th Lesson

I. Mechanical Properties of Fluids Multiple Choice Questions (1 Mark)

Question 1.
The rise of a liquid in a capillary tube does not depends on………
(1) angle of contact
(2) density
(3) outer radius of the capillary tube
(4) surface tension
Answer:
(3) outer radius of the capillary tube

Question 2.
The type of flow is characterized by parallel layers of fluid moving with out mixing is………
(1) Streamline flow
(2) Turbulent flow
(3) Circular flow
(4) Rotational flow
Answer:
(1) Streamline flow

Question 3.
The angle of contact between pure water and clean glass is………
(1) 90°
(2) 0°
(3) 135°
(4) 180°
Answer:
(2) 0°

Question 4.
Bernoulli’s principle is based on the conservation of……………..
(1) Momentum
(2) Angular momentum
(3) Energy
(4) Volume
Answer:
(3) Energy

Question 5.
Among the following, the wrong statement about pressure is………….
(1) It is a vector quantity
(2) It is a scalar quantity
(3) Pressure at sea level is 1.013 x 10⁵Pa.
(4) Dimensions of pressure are [ML^-1T^-2]
Answer:
(1) It is a vector quantity

Question 6.
The gauge pressure at a depth of 10 m in a lake is…………..
(1) 10⁶ Pa
(2) 10⁵ Pa
(3) 10⁴ Pa
(4) Zero
Answer:
(2) 10⁵ Pa

Question 7.
Surface tension arises due to………….
(1) gravitational forces
(2) pressure differences
(3) viscosity
(4) cohesive forces
Answer:
(4) cohesive forces

Question 8.
Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in……………..
(1) temperature
(2) viscosity
(3) pressure
(4) flow rate
Answer:
(3) pressure

Question 9.
The terminal velocity of a sphere of radius R falling in a viscous fluid is proportional to………….
(1) R
(2) R³
(3) √R
(4) R²
Answer:
(4) R²

Question 10.
1 torr is equal to………..
(1) 1.013 x 10⁵ Pa
(2) 760 Pa
(3) 133 Pa
(4) 1013 Pa
Answer:
(3) 133 Pa

II. Mechanical Properties of Fluids Fill in the Blanks (1 Mark)

Question 1.
The difference between absolute pressure (P) and atmospheric pressure (P_a) at depth h is called……..
Answer:
Gauge pressure

Question 2.
1 bar is equal to ………… Pa
Answer:
10⁵

Question 3.
Hydraulic lift and hydraulic brakes are based on ………… law.
Answer:
Pascal’s

Question 4.
The study of fluids in motion is known as ………….
Answer:
fluid dynamics

Question 5.
The path taken by a fluid particle under a steady flow is called a ………….
Answer:
streamline

Question 6.
The Bernoulli’s equation in general can be written as ………….
Answer:
(P+\(\frac{1}{2} \)ρV²+ρgh=constant)

Question 7.
The maximum velocity acquired by a falling sphere in a viscous fluid is called …………
Answer:
terminal velocity

Question 8.
The SI unit of surface tension is ………….
Answer:
N/Du

Question 9.
The spherical shape of raindrops is due to ………….
Answer:
surface tension

Question 10.
The aerodynamic lift experienced by a spinning ball moving in air is called ………….
Answer:
magnus effect

III. Mechanical Properties of Fluids One Word Answer Questions (1 Mark)

Question 1.
What is relative density ?
Answer:
Ratio

Question 2.
Name the device used to measure atmospheric pressure.
Answer:
Barometer

Question 3.
Write the equation of continuity.
Answer:
A₁ v₁= A₂ v₂

Question 4.
Mention the speed limit, beyond which steady flow of liquid becomes turbulent?
Answer:
Reynolds

Question 5.
What is the speed of efflux from a hole at the bottom of a tank filled with water to a height h, which is open at the top?
Answer:
√2gh

Question 6.
What is the property of a fluid to resist relative motion between its layers ?
Answer:
Viscosity

Question 7.
Which principle is involved in the dynamic lift of an airplane ?
Answer:
Bernoulli

Question 8.
What happens to the viscosity of liquids with increase in temperature?
Answer:
Decreases

Question 9.
What is the SI unit of the coefficient of viscosity ?
Answer:
Decreases

Question 10.
What is surface tension?
Answer:
Cohesion

IV. Mechanical Properties of Fluids Very Short Answer Questions (2 Marks)

Question 1.
Define average pressure. Is it a scalar or a vector quantity ?
Answer:
It is defined as the total normal force acting per unit area:
P=\(\frac{F}{A}\)
It is a scalar quantity because it has magnitude but no specific direction.

Question 2.
What is the Magnus effect ?
Answer:
When the ball is spinning and moving in air, it experience a net upward force called dynamic lift. This dynamic lift due to spinning is called “Magnus effect”.

Question 3.
Why are liquid drops and bubbles spherical ?
Answer:
Due to surface tension, the free surface of liquids tend to contract to have minimum surface area. For a given volume sphere possesses minimum surface area. Hence drops and bubbles are spherical.

Question 4.
Give the expression for the excess pressure in a liquid drop.
Answer:
ΔP= \(R \frac{2T}{R}\)
Where T is surface tension and R is the radius.

Question 5.
Give the expression for the excess pressure in an air bubble inside the liquid.
Answer:
ΔP = \(\frac{2 \mathrm{~T}}{\mathrm{R}}\)
Same as a liquid drop since only one surface contributes.

Question 6.
Give the expression for the excess pressure in a soap bubble in air.
Answer:
ΔP= \(\frac{4 \mathrm{~T}}{\mathrm{R}}\)
Because the soap bubble has two surfaces (inner and outer) in contact with air.

Question 7.
What is the angle of contact ?
Answer:
The angle between the tangent to the liquid surface and the solid surface, at the point of contact, inside the liquid is known as angle of contact.

Question 8.
Mention two examples that obey Bernoulli’s theorem and justify them.
Answer:

• Airplane Wings : Faster airflow above the wing causes lower pressure, generating lift.
• Atomizer : Fast air over a tube reduces pressure and draws liquid up.

Question 9.
When water flows through a pipe, which layers move fastest and slowest?
Answer:
In laminar flow, the central layer moves fastest due to less resistance, while the layer near the wall moves slowest due to friction.

Question 10.
Explain why terminal velocity is higher for a body with a larger surface area.
Answer:
A body with larger surface area experiences greater viscous drag, which balances weight faster, but also increases buoyant force. Terminal velocity depends on density contrast and shape, not just surface area.

Example:
Consider three vessels A, B and C of different shapes. They are connected at the bottom by a horizontal pipe. On filling with water the level in the three vessels is same though they hold different amount of water. This is because water at the bottom has the same pressure below each section of the vessel.

Question 6.
Explain how pressure varies with depth in a liquid.
Answer:
Pressure in a liquid increases linearly with depth:
P= P_o+ρgh
Where ρ is density, g is gravity, and h is depth. It’s independent of container shape.

Question 7.
What is Torricelli’s law? How the speed of efflux is determined experimentally?
Answer:
Torricelli’s law : The speed of efflux from an orifice at the side of container at a depth ‘h’ below the free surface of a liquid is equal to the speed gained by a freely falling body after when it falls through a distance ‘ h’.
It states that the speed of efflux from a small hole in a tank is v=√2ghv
It is verified by measuring the horizontal range of water jet falling from a known height h. The above equation is known as Torricelli’s law.

Question 8.
Explain dynamic lift with examples.
Answer:
Dynamic lift : It is defined as the upthrust acting on a body when it is moving in air.
Examples :

• Airplane wings: Faster air over the curved top creates lower pressure.
• Spinning balls: The Magnus effect causes curved trajectories.

Question 9.
Explain surface tension and surface energy.
Answer:

• Surface Tension : The tangential force per unit length, acting at right angles on either side of a line imagined to be drawn on the free liquid surface in equilibrium is called surface tension.
• Surface Energy : The additional potential energy due to the molecular forces per unit surface area is called surface energy.

Surface Energy =\(\frac{\text { Potential energy due to molecular forces }}{\text { Surface area }}\)

Question 10.
Explain how surface tension is measured experimentally.
Answer:
Surface tension is measured using a capillary rise method, where liquid rises in a tube.
Using the height of rise, radius of tube, and density of liquid, T is calculated from :
T = \(\frac{\text { rhpg }}{2}\)

V. Mechanical Properties of Fluids Short Answer Questions (4 Marks)

Question 1.
State Bernoulli’s principle. From conservation of energy in a fluid flow through a tube, derive Bernoulli’s equation. Give an application of Bernoulli’s theorem.
Answer:
Bernoulli’s Principle : “When an incompressible and non viscous fluid flowing steadily through a tube of non uniform area of cross section, then at every point in the path of the fluid, the total energy per unit volume remains constant.”
(OR)
In the stream line flow, the sum of pressure energy, kinetic energy and potential energy per unit volume remains constant.
Mathematically,

∴ This is Bernoulli’s equation. It is strictly valid for incompressible non viscous and steady flow.

Application :
a) Venturimeter
b) Carburetor
c) Dynamic lift on an air foil (aerodynamic lift)
d) Dynamic lift on a spinning ball moving in air (magnus effect)

Question 2.
Define the coefficient of viscosity. Explain Stoke’s law and derive the expression for terminal velocity. Discuss the conditions under which a rain drop attains terminal velocity.
Answer:
Co – efficient of viscosity (η) : It is defined as the ratio of shearing stress to the strain rate.
η=\(\frac{\mathrm{F} / \mathrm{A}}{\mathrm{v} / \mathrm{l}}=\frac{\mathrm{Fl}}{\mathrm{vA}}\)
Where, F-Tangential viscous force
A – Area of the layer
v – Velocity of the layer
l – Thickness of liquid film
SI unit : Ns/m² or Pas
CGS unit : poise
Dimensional Formula : ML^-1 T^-1
Stoke’s law : When a body falls through a fluid, it drags the layer of the fluid in contact with it. A relative motion between the different layers of the fluid is formed and the body experiences a retarding force.

Example :

• Falling of a rain drop.
• Swinging of simple pendulum in air in this motion.

Viscous force F=6 πηav
Where 6 π is constant of proportionality. This is known as stoke’s law.
Terminal Velocity: It is the constant velocity of a body attains when net force becomes zero. For a falling sphere vt= \(\frac{2 \pi^{\mathrm{r}}(\rho-\sigma) \mathrm{g}}{9 \eta}\)
Where,
ρ – Density of object
σ – Density of fluid
A raindrop attains terminal velocity when the downyward gravitational force is exactly balanced by the sum of buoyant force and viscous drag.

VI. Mechanical Properties of Fluids Long Type Questions (8 Marks)

Question 1.
Calculate the work done in blowing a soap bubble of diameter 0.6 cm against the surface tension force. (Surface tension of soap solution T=2.5 ×10² Nm¹
Answer:
Given
Diameter d = 0.6 cm
Radius (r)=0.30m=3 x 10^-3m
Workdone in blowing a soap bubble =8 πr² T
=8 × 3.14 × left(3 × 10^-3)² × 2.5 × 10^-2
=8 × 3.14 × 9 ×10^-6 × 2.5 ×10^-2
=5.65 × 10^-6J

Question 2.
How high does methyl alcohol rise in a glass tube of diameter 0.06 cm ? (Surface tension Tof methyl alcohol =0.023 Nm^-1, density =0.8g/ cm³, angle of contact is zero)
Answer:
Given
Diameter =0.06 cm
Radius (r) =0.03cm=3 × 10^-4 m

Question3.
What should be the radius of a capillary tube if water rises to a height of 6 cm in it? (Surface tension of water T=7.2× 10² Nm^-1
Answer:
Given
h=6 cm=6 x10^-2m
g=9.8 m/s²
Surface Tension & T=7.2 x 10² N/m
Density of water & d=1000=10³ kg/m
r=?

Question 4.
Find the depression of the meniscus in a capillary tube of diameter 0.4 mm dipped in mercury. (Density of mercury ρ=13.6 × 10³ kgm³, surface tension of mercury =0.49 Nm′ and angle of contact 135°)
Answer:
Given,
Diameter =0.4 mm
Radius r =0.2 mm
r=0.2 × 10^-3 m=2 ×10^-4 m
Density of mercury, ρ=13.6 × 10³ kg/m³
Surface Tension, T=0.49 N/ m
Angle of contact, σ=135°
g=9.8 m/s²
Depression, h= ?

Question 5.
If the diameter of a soap bubble is 10 mm and its surface tension is 0.04 Nm¹, find the excess pressure inside the bubble.
Answer:
Given
Diameter, (d) =10mm
Radius, (r)=5 mm=5 ×10^-3 m
Surface Tension, (T)=0.04 N/m
Excess pressure in a bubble,

Question 6.
If the work done to form a bubble of radius R is W, find the energy required to increase its radius to 2R.
Answer:
Given,
Workdone to form a bubble of radius R is W
W=8 π R²T……………….(1)
Energy required to increase its radius from R to 2R
= 8 πT[(2R)² – R²]
= 8 πT [3R²]
= 3 × 8 πR²T
= 3W [∵ From (1)]

Question 7.
If two soap bubbles of radii R₁ and R₂ (in vacuum) coalesce under isothermal conditions, find the radius of the resulting bubble. Take T as the surface tension of soap solution.
Answer:
Workdone to form bubble to radius R₁+ Workdone to form bubble of radius
R₂ = Workdone to form new bubble of radius R