A horizontal pipe of cross-sectional diameter 5 cm carries water at velocity of $4{\rm{m}}{{\rm{s}}^{ - 1}}$. The pipe is connected to a smaller pipe with a cross-sectional diameter 4 cm. the velocity of water through the smaller pipe is

$6.25{\rm{m}}{{\rm{s}}^{ - 1}}$

$2.56{\rm{m}}{{\rm{s}}^{ - 1}}$

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NEET • PHYSICS • MECHANICAL PROPERTIES OF FLUIDS

Mechanical properties of fluids practice · Mixed difficulty

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Showing 1-30 of 313 questions

1 Medium

1 of 313

Remembering +4 | -1

With the increase in temperature viscosity of a liquid -

View answer and explanation

Correct option: B

Decreases

Option B (Decreases) is correct because as temperature increases, the cohesive forces between liquid molecules weaken, reducing viscosity.

2 Medium

2 of 313

Understanding +4 | -1

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: When you squeeze one end of a tube to get toothpaste out from the other end, Pascal's principle is observed.

Reason R: A change in the pressure applied to an enclosed incompressible fluid is transmitted undiminished to every portion of the fluid and to the walls of its container.

In the light of the above statements, choose the most appropriate answer from the options given below.

View answer and explanation

Correct option: D

Both A and R is correct and R is the correct
explanation of A

The correct answer is D because Assertion A correctly describes an application of Pascal's principle, and Reason R accurately states Pascal's principle, which explains why squeezing the tube results in toothpaste coming out.

3 Medium

3 of 313

Remembering +4 | -1

Hydraulic lifts and hydraulic brakes are based
on

View answer and explanation

Correct option: D

Pascal's law

Option D (Pascal's law) is correct because hydraulic lifts and brakes operate based on the principle of pressure transmission in fluids, as described by Pascal's Law.

4 Easy

4 of 313

Understanding +4 | -1

As the temperature of a liquid is raised, the coefficient of viscosity

View answer and explanation

Correct option: A

decreases

Option A (decreases) is correct because as the temperature of a liquid increases, the cohesive forces between its molecules weaken, leading to a decrease in viscosity.

5 Medium

5 of 313

Application +4 | -1

A horizontal pipe of cross-sectional diameter 5 cm carries water at velocity of

4\mathrm{m}{\mathrm{s}^{ - 1}}

. The pipe is connected to a smaller pipe with a cross-sectional diameter 4 cm. the velocity of water through the smaller pipe is

View answer and explanation

Correct option: A

6.25\mathrm{m}{\mathrm{s}^{ - 1}}

Option A (

6.25\mathrm{m}{\mathrm{s}^{ - 1}}

) is correct because it is calculated using the principle of continuity (A1V1 = A2V2).

6 Medium

6 of 313

Understanding +4 | -1

If two soap bubble of different radii are connected by a tube

View answer and explanation

Correct option: C

Air flows from the smaller bubble to the bigger

Option C is correct. Air flows from the smaller bubble to the bigger bubble because the pressure inside the smaller bubble is higher.

7 Medium

7 of 313

Application +4 | -1

The fraction of a floating object of volume

{V_0}

and density

{d_0}

above the surface of a liquid of density

d

will be

View answer and explanation

Correct option: C

\frac{{d - {d_0}}}{d}

Option C (

\frac{{d - {d_0}}}{d}

) is correct because the fraction above the surface is the ratio of the difference between the liquid's density and the object's density to the liquid's density.

8 Medium

8 of 313

Application +4 | -1

Air is streaming past a horizontal air plane wing such that its speed is

120\mathrm{m}{\mathrm{s}^{ - 1}}

over the upper surface and

90\mathrm{m}{\mathrm{s}^{ - 1}}

at the lower surface. If the density of air is

1.3\mathrm{kg}{\mathrm{m}^{ - 3}}

, what will be the gross life on the wing? If the wing is

10\mathrm{m}

long and has an average width of 2 m,

View answer and explanation

Correct option: C

81.9 kN

Option D (

128 \sqrt{\frac{2h}{g}}

) is correct because the time taken for the water level to decrease is calculated by integrating the rate of efflux over the given height range, considering the changing cross-sectional area.

9 Easy

9 of 313

Application +4 | -1

The density of ice is

x \mathrm{~g} \mathrm{~cm}^{-3}

and that of water is

y \mathrm{~g} \mathrm{~cm}^{-3}

. When

m

gram of ice melts, then the change in volume is

View answer and explanation

Correct option: D

\frac{m}{y}-\frac{m}{x}

Option D (

\frac{m}{y}-\frac{m}{x}

) is correct because the change in volume is the difference between the volume of water and the volume of ice.

10 Easy

10 of 313

Understanding +4 | -1

If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container is

View answer and explanation

Correct option: C

90^{\circ}

Option C is correct. When the surface of a liquid is plane, it neither wets nor is repelled by the container walls, resulting in a 90-degree angle of contact.

11 Medium

11 of 313

Application +4 | -1

Fermer bone has base

\mathrm{n}

average cross section area

100 \mathrm{~cm}^2

supporting mass of

40 \mathrm{~kg}

of man find average pressure

View answer and explanation

Correct option: A

4 \times 10^4

Option A (

4 \times 10^4

) is correct because the average pressure is calculated by dividing the force (weight) by the area, resulting in approximately

4 \times 10^4

Pa.

12 Medium

12 of 313

Analyzing +4 | -1

A small iron sphere is dropped from a great height. It attains its terminal velocity after having fallen 32 m. Then, it covers the rest of the path with terminal velocity only. The work done by air friction during the first 32 m of fall is

{W_1}

. The work done by air friction during the subsequent 32 m fall is

{W_2}

. Then

View answer and explanation

Correct option: B

{W_1} < {W_2}

Option B (directly proportional to both radius

R

and velocity

v

) is correct because Stokes' law states that the viscous force is directly proportional to both radius and velocity.

13 Medium

13 of 313

Understanding +4 | -1

Assertion: Pressure is a vector quantity.

Reason: Pressure

P=\frac{F}{A}

. Here

F

, the force is a vector quantity.

View answer and explanation

Correct option: D

If Assertion is false but the Reason is true

Option D (If Assertion is false but the Reason is true) is correct because pressure is a scalar quantity, not a vector, but the formula P=F/A is correct.

14 Medium

14 of 313

Analyzing +4 | -1

A: Kerosene Oil spreads out over water surface
R: Surface tension is a surface phenomenon

View answer and explanation

Correct option: C

A is true but R is false

Option D (

9v

) is correct because the terminal velocity is proportional to the square of the radius.

15 Medium

15 of 313

Analyzing +4 | -1

A metallic wire of diameter '

d

' is lying horizontally on the surface of water. The maximum length of wire so that it may not sink will be

View answer and explanation

Correct option: D

Any length

The correct answer is Any length because the surface tension force acts along the length of the wire, and as long as the wire is carefully placed, it can be supported regardless of its length.

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16 Medium

16 of 313

Understanding +4 | -1

On which of the following, the terminal velocity of a solid ball in a viscous fluid is independent?

View answer and explanation

Correct option: B

Height of the liquid

Option B (Height of the liquid) is correct because terminal velocity depends on factors like viscosity, density of the ball and liquid, and radius of the ball, but not the height of the liquid column.

17 Medium

17 of 313

Remembering +4 | -1

Pressure applied to enclosed fluid is:

View answer and explanation

Correct option: D

Transmitted unchanged to every portion of the fluid and wall of containing vessel

Option D is correct because Pascal's Law states that pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

18 Medium

18 of 313

Analyzing +4 | -1

A boat carrying a number of large stones is floating in a water tank. What would happen to the water level, if a few stones are unloaded into water?

View answer and explanation

Correct option: B

Falls

Option B (Falls) is correct because the stones displace their weight in water while in the boat, but only their volume when unloaded, and stones are denser than water.

19 Medium

19 of 313

Analyzing +4 | -1

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : Product of Pressure

\left( P \right)

and time

\left( t \right)

has the same dimension as that of coefficient of viscosity.
Reason R : Coefficient of viscosity

= \frac{{{\text{Force}}}}{{{\text{Velocity}}\,\,\,{\text{gradient}}}}

Choose the correct answer from the options given below.

View answer and explanation

Correct option: C

A is true but R is false

Option C (surface tension) is correct because surface tension minimizes the surface area of a liquid, leading to a spherical shape.

20 Easy

20 of 313

Understanding +4 | -1

In which flow the velocity of fluid particles reaching a particular point is same at all time?

View answer and explanation

Correct option: B

steady flow

Option B (steady flow) is correct. In steady flow, the velocity of fluid particles at a particular point remains constant over time.

21 Medium

21 of 313

Application +4 | -1

A vessel, whose boom has round holes with a diameter of 0.1mm, is filled with water. The maximum height to which the water can be filled without leakage is (S.T. of water =

75\mathrm{ }dyne/cm,\mathrm{ }g\mathrm{ } = 1000\mathrm{ }cm/{s^2}

)

View answer and explanation

Correct option: D

30 cm

Option D (30 cm) is correct because the maximum height is determined by balancing the pressure due to the water column with the pressure due to surface tension.

22 Medium

22 of 313

Understanding +4 | -1

An air-tight cage with a parrot sitting in it is suspended from the spring balance. The parrot starts flying. The reading of the spring balance will

View answer and explanation

Correct option: C

Not change

Option C (Not change) is correct because the spring balance measures the total weight of the cage and parrot, which remains constant whether the parrot is sitting or flying.

23 Easy

23 of 313

Understanding +4 | -1

100 drops of a liquid coalesce to form a single drop under isothermal condition. In this process energy is

View answer and explanation

Correct option: B

Released

Option B is correct. When smaller drops coalesce into a larger drop, the surface area decreases, releasing energy due to surface tension.

24 Medium

24 of 313

Application +4 | -1

A beaker containing a liquid of density

\rho

moves up with an acceleration a. The pressure due to the liquid at a depth h below the free surface of the liquid is

View answer and explanation

Correct option: B

h\rho \left( {g + a} \right)

Option B (

h\rho \left( {g + a} \right)

) is correct because the effective acceleration due to gravity increases when the beaker accelerates upwards, resulting in a higher pressure.

25 Easy

25 of 313

Remembering +4 | -1

Pressure inside a soap bubble is greater than the pressure outside by an amount :

(given :

\mathrm{R}=

Radius of bubble,

\mathrm{S}=

Surface tension of bubble)

View answer and explanation

Correct option: A

\frac{4 \mathrm{S}}{\mathrm{R}}

Option A is correct. The excess pressure inside a soap bubble is given by the formula

\frac{{4S}}{{R}}

26 Medium

26 of 313

Application +4 | -1

Water has been filled in a vertical capillary tube upto the top after closing its lower end by a finger Consider radius of capillary r = 1 mm, surface tension is 70 dyne/cm and g = 980 cm/sec . Which of the option is correct when finger is removed?

View answer and explanation

Correct option: D

Nearly 2.86 cm of water will stay inside the capillary tube and rest will fall down.

Option D (Nearly 2.86 cm of water will stay inside the capillary tube and rest will fall down) is correct because the height to which water rises in a capillary tube is given by

h = \frac{{2T\cos\theta}}{{r\rho g}}

, and this height remains even after removing the finger.

27 Medium

27 of 313

Understanding +4 | -1

Water enters through end

A

with speed

v_1

and leaves through end B with speed

v_2

of a cylindrical tube AB. The tube is always completely filled with water. In case I tube is horizontal and in case II it is vertical with end A upwards and in case III it is vertical with end

B

upwards. We have

v_1=v_2

for

View answer and explanation

Correct option: D

Each case

Option D (Each case) is correct because the principle of continuity states that for an incompressible fluid in a closed system, the volume flow rate must remain constant, regardless of the tube's orientation.

28 Easy

28 of 313

Application +4 | -1

Two capillaries P and Q are dipped in water. The height of water level in capillary P is 2/3 to the height in Q capillary. The ratio of diameter is

View answer and explanation

Correct option: B

0.126388889

Answer A (0.085416667) is incorrect. Answer B (0.126388889) is correct because the height of the water level is inversely proportional to the radius (or diameter) of the capillary tube.

29 Medium

29 of 313

Remembering +4 | -1

One of the units earlier used for expressing pressure was called bar. 1 bar is equivalent to:

View answer and explanation

Correct option: B

10^5 \mathrm{~Pa}

Option B (

10^5 \mathrm{~Pa}

) is correct because 1 bar is defined as

10^5

Pascals.

30 Medium

30 of 313

Remembering +4 | -1

In stream line flow of liquid, the total energy of liquid is constant at

View answer and explanation

Correct option: A

all points

Option A (all points) is correct because, by definition, in streamline flow, the total energy (pressure, kinetic, and potential) of the fluid remains constant along each streamline.

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