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NEET • PHYSICS • MECHANICAL PROPERTIES OF FLUIDS

Mechanical properties of fluids practice · Easy

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1 Easy

1 of 61

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.

2 Easy

2 of 61

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.

3 Easy

3 of 61

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.

4 Easy

4 of 61

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.

5 Easy

5 of 61

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.

6 Easy

6 of 61

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}}

7 Easy

7 of 61

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.

8 Easy

8 of 61

Application +4 | -1

The angle of contact between glass and water is

0^\circ

and it rises in a capillary up to 6 cm when its surface tension is 70 dynes/cm. Another liquid of surface tension 140 dyne/cm angle of contact

60^\circ

and relative density 2 will rise in the same capillary by

View answer and explanation

Correct option: C

3 cm

Option C (3 cm) is correct because it is calculated by comparing the capillary rise equations for the two liquids, considering the differences in surface tension, angle of contact, and density.

9 Easy

9 of 61

Remembering +4 | -1

Bernoulli's equation is based on the principle of

View answer and explanation

Correct option: B

Conservation of energy

Option B (Conservation of energy) is correct. Bernoulli's equation is a direct application of the principle of conservation of energy to fluid flow.

10 Easy

10 of 61

Application +4 | -1

A big drop of radius

R

is formed by 1000 small droplets of water, then the radius of small drop is

View answer and explanation

Correct option: D

R / 10

Option D (

R/10

) is correct because the volume of the big drop equals the sum of the volumes of the 1000 small droplets.

11 Easy

11 of 61

Understanding +4 | -1

The surface tension of liquid at its boiling point

View answer and explanation

Correct option: A

becomes zero

Option A (becomes zero) is correct because at the boiling point, the intermolecular forces weaken significantly, reducing surface tension to zero.

12 Easy

12 of 61

Application +4 | -1

An object having total volume of

10 {~m}^3

is floating and it is just completely immersed in a fluid of density

0.5 {~g} / {cc}

. Buoyant force acting on the object is

\left(g=10 {~m} / {s}^2\right)

View answer and explanation

Correct option: C

5 \times 10^4 {~N}

Option C (

5 \times 10^4 {~N}

) is correct because the buoyant force is equal to the weight of the fluid displaced by the object, which is the product of the fluid's density, the object's volume, and the acceleration due to gravity.

13 Easy

13 of 61

Understanding +4 | -1

Consider the two statements:
Statement-1: A capillary tube is frst dipped in hot water and then dipped in cold water. The rise is higher in hot water.
Statement-2: Capillary tube is first dipped in cold water and then dipped in hot water. The rise is higher in cold water.

View answer and explanation

Correct option: B

Statement-1 is false and statement-2 is true

Option B is correct. Surface tension decreases with increasing temperature, so the capillary rise is higher in cold water.

14 Easy

14 of 61

Application +4 | -1

The surface energy of liquid film on a ring of area

0.15\,{m^2}

is (T=5 N/m)

View answer and explanation

Correct option: B

1.5 J

Option B (1.5 J) is correct because the surface energy is calculated by multiplying the surface tension by twice the area of the film.

15 Easy

15 of 61

Application +4 | -1

A body measures

5 \mathrm{~N}

in air and

2 \mathrm{~N}

when put in water. The buoyant force is

View answer and explanation

Correct option: C

3 \mathrm{~N}

Option C (3 N) is correct because the buoyant force is the difference between the weight in air and the weight in water.

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16 Easy

16 of 61

Remembering +4 | -1

Which among the following is incorrect?

View answer and explanation

Correct option: D

1 torr

=76 {~cm}

{Hg}

The incorrect statement is D because 1 torr is approximately 1 mm of Hg, not 76 cm of Hg. 76 cm of Hg is equal to 1 atm.

17 Easy

17 of 61

Application +4 | -1

A wooden cube floating in water supports a mass of

m=0.2 {~kg}

on its top. When the mass is removed, the cube rises by

2 {~cm}

. The side of the cube is

\left(\rho_{\text {water }}\right.

=10^3 {~kg} / {m}^3

)

View answer and explanation

Correct option: D

10 {~cm}

The side of the cube is 10 cm. The weight of the mass is equal to the buoyant force due to the submerged volume of the cube. By equating these, the side of the cube can be found.

18 Easy

18 of 61

Understanding +4 | -1

If a soap bubble expands, the pressure inside the bubble:

View answer and explanation

Correct option: B

decreases

Option B is correct. As a soap bubble expands, its radius increases, and the pressure inside decreases according to

P = \frac{{4T}}{r}

19 Easy

19 of 61

Application +4 | -1

The cross sections of a pipe at two points A and B are in the ratio 1:4. If the speed of water flowing through the pipe at point A is V, its speed at point B is

View answer and explanation

Correct option: B

\frac{V}{4}

Option B (

\frac{{V}}{{4}}

) is correct because, according to the equation of continuity, the speed of the fluid is inversely proportional to the cross-sectional area.

20 Easy

20 of 61

Application +4 | -1

A tank containing water has an orifice in one vertical side. It is 10 m below the surface level of water in tank. Then velocity of efflux from that small orifice is [in m/s]

View answer and explanation

Correct option: D

Option D (14 m/s) is correct because the velocity of efflux is calculated using Torricelli's theorem, which states that the velocity is equal to the square root of 2gh.

21 Easy

21 of 61

Application +4 | -1

An open water tank is placed on a platform of height

16 {~m}

from ground. Height of water in tank is

12 {~m}

from its base and it is filled completely with water. Height of a small hole, from ground which should be made on wall of container so that water strikes at maximum distance from base of platform on ground is

View answer and explanation

Correct option: D

16 {~m}

Option D (16 m) is correct because the maximum range is achieved when the hole is at half the height of the water level above the point where the water lands, which in this case is the ground.

22 Easy

22 of 61

Application +4 | -1

When two liquids of same mass but different densities are mixed together, then the density of the mixture is

View answer and explanation

Correct option: B

\frac{2 \rho_1 \rho_2}{\rho_1+\rho_2}

Option B (

\frac{2 ho_1 ho_2}{\rho_1+\rho_2}

) is correct because the density of the mixture is the total mass divided by the total volume, and the masses are equal.

23 Easy

23 of 61

Application +4 | -1

A needle of length 5 cm is floating on water of surface tension

0.07\,J{m^{ - 2}}

and is not wetted by water. Then the weight of the needle will be (take

g = 10\,m/{s^2}

)

View answer and explanation

Correct option: B

0.7 \times {10^{ - 3}}\,kg\,wt

Option B (

0.7 \times {10^{ - 3}}\,kg\,wt

) is correct because the weight of the needle is balanced by the force due to surface tension acting on both sides of the needle.

24 Easy

24 of 61

Application +4 | -1

A barometer kept in an elevator reads

76 {~cm}

{Hg}

when elevator is accelerating upwards. Possible value of pressure inside the elevator is (in

{cm}

{Hg})

View answer and explanation

Correct option: A

Option A (78) is correct because when the elevator accelerates upwards, the effective gravity increases, leading to a higher barometer reading.

25 Easy

25 of 61

Understanding +4 | -1

Coatings used on raincoat are waterproof because they

View answer and explanation

Correct option: A

increases angle of contact

Option A (increases angle of contact) is correct because a larger contact angle makes it harder for water to spread on the fabric, thus making it waterproof.

26 Easy

26 of 61

Application +4 | -1

If a capillary tube is tilted to

45^\circ \,\mathrm{and}\,\,60^\circ

from the vertical then the ratio of length

{l_1}\,{l_2}

of liquid columns in it will be

View answer and explanation

Correct option: A

1:\sqrt 2

Option B (

\sqrt 2 :1

) is correct because the length of the liquid column is inversely proportional to the cosine of the angle from the vertical.

27 Easy

27 of 61

Application +4 | -1

The pressure on the top surface of an aeroplane wing was

0.90 \times {10^5}\,Pa

and at the bottom surface is

0.91 \times {10^5}\,Pa.

If the area of each surface is

40\,{m^2},

the net lift force on the wing is

View answer and explanation

Correct option: D

4 \times {10^4}\,N

Option D (

4 \times {10^4}\,N

) is correct because the net lift force is the product of the pressure difference and the area of the wing.

28 Easy

28 of 61

Understanding +4 | -1

Water does not wet an oily glass because

View answer and explanation

Correct option: D

cohesive force of water

>

adhesive force between water and oil molecules

Option D is correct because the cohesive forces within water are stronger than the adhesive forces between water and oil, preventing wetting.

29 Easy

29 of 61

Understanding +4 | -1

Due to capillary action, a liquid will rise in a tube. If the angle of contact is

View answer and explanation

Correct option: A

Acute

Option A is correct because a liquid rises in a tube due to capillary action when the angle of contact is acute (less than 90 degrees), indicating adhesive forces are stronger than cohesive forces.

30 Easy

30 of 61

Remembering +4 | -1

In Bernoulli’s theorem which of the following is conserved?

View answer and explanation

Correct option: C

Energy

Option C (Energy) is correct. Bernoulli's theorem is a statement of the conservation of energy for flowing fluids.

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Key Takeaways

✓ This set contains 61 single-correct-answer MCQs on MECHANICAL PROPERTIES OF FLUIDS.
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