An object weights $m_1$ in a liquid of density $d_1$ and that in liquid of density $d_2$ is $m_2$. The density of th object is

$\frac{m_2 d_2-m_1 d_1}{m_2-m_1}$

$\frac{m_1 d_1-m_2 d_2}{m_2-m_1}$

$\frac{m_2 d_1-m_1 d_2}{m_1-m_2}$

Water is moving with a speed of $5.18{\rm{m}}{{\rm{s}}^{ - 1}}$ through a pipe with a cross-sectional area of $4.20{\rm{c}}{{\rm{m}}^2}$. The water gradually descend 9.66 m as the pipe increase in area to $7.60{\rm{c}}{{\rm{m}}^2}$ . The speed of flow at the lower level is

$2.86{\rm{m}}{{\rm{s}}^{ - 1}}$

$3.82{\rm{m}}{{\rm{s}}^{ - 1}}$

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JEE • PHYSICS • MECHANICAL PROPERTIES OF FLUIDS

Mechanical properties of fluids practice · Medium

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Practice format and chapter quiz

These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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Showing 1-30 of 390 questions

1 Medium

1 of 390

Application +4 | -1

The average mass that must be lifted by a hydraulic press is

80 \mathrm{~kg}

. If the radius of the larger piston is five times that of the smaller piston, what is the minimum force that must be applied?

View answer and explanation

Correct option: A

31.4 \mathrm{~N}

Option A (

31.4 \mathrm{~N}

) is correct because it is the minimum force calculated using Pascal's principle for hydraulic presses, where the force is proportional to the area of the piston.

2 Medium

2 of 390

Understanding +4 | -1

A small drop of oil spreads over water because

View answer and explanation

Correct option: B

water has a higher surface tension

Option B is correct because oil spreads over water due to water having a higher surface tension than oil.

3 Medium

3 of 390

Application +4 | -1

A film of water is formed between two straight parallel wires of length

20 \mathrm{~cm}

with separation of

0.5 \mathrm{~cm}

. The work done to increase the separation by

0.1 \mathrm{~cm}

is:

View answer and explanation

Correct option: B

28 \times 10^{-6} \mathrm{~J}

Option B (

28 \times 10^{-6} \mathrm{~J}

) is correct because it is the work done to increase the separation, calculated using the surface tension and the change in surface area.

4 Medium

4 of 390

Application +4 | -1

The velocity of water in a river is

15 \mathrm{~m} / \mathrm{s}

near the surface. If the river is

5 \mathrm{~m}

deep, find the shearing stress between the horizontal layers of water. The coefficient of viscosity of water

=10^{-2}

poise.

View answer and explanation

Correct option: C

3 \times 10^{-3} \mathrm{~N} / \mathrm{m}^2

Option C (

3 \times 10^{-3} \mathrm{~N} / \mathrm{m}^2

) is correct because it is calculated using the formula for shearing stress involving viscosity and velocity gradient.

5 Medium

5 of 390

Application +4 | -1

A liquid rises to a height of 2 cm in a capillary tube. The angle of contact between the solid and the liquid is zero. The tube is depressed more so that the top of capillary tube is only one cm above the liquid. Then the apparent angle of contact between the solid and liquid is

View answer and explanation

Correct option: C

60^\circ

Option C (

60^\circ

) is correct because it is calculated using the relation between height, angle of contact, and surface tension in a capillary tube.

6 Medium

6 of 390

Application +4 | -1

An object weights

m_1

in a liquid of density

d_1

and that in liquid of density

d_2

m_2

. The density of th object is

View answer and explanation

Correct option: D

\frac{m_1 d_2-m_2 d_1}{m_1-m_2}

Option D (

\frac{m_1 d_2-m_2 d_1}{m_1-m_2}

) is correct because it is derived from the buoyant force equations in two different liquids and solving for the density of the object.

7 Medium

7 of 390

Understanding +4 | -1

A liquid does not wet the sides of a solid, if the angle of contact is

View answer and explanation

Correct option: A

Obtuse

Option A (Obtuse) is correct because a liquid does not wet the sides of a solid if the cohesive forces within the liquid are stronger than the adhesive forces between the liquid and the solid, resulting in an obtuse angle of contact.

8 Medium

8 of 390

Understanding +4 | -1

The quantity

\frac{\rho \mathrm{v D}}{\eta}

(Reynold's number) is ____.

View answer and explanation

Correct option: A

Dimensionless

Option A (Dimensionless) is correct because the Reynolds number is a dimensionless quantity used to predict flow patterns.

9 Medium

9 of 390

Application +4 | -1

The terminal velocity

v

of a spherical ball of lead of radius

R

falling through a viscous liquid varies with

R

such that

View answer and explanation

Correct option: D

\frac{v}{{{R^2}}} =

constant

Option D (

\frac{v}{{{R^2}}} =

constant) is correct because the terminal velocity of a spherical ball falling through a viscous liquid is directly proportional to the square of the radius.

10 Medium

10 of 390

Application +4 | -1

A cubical block of wood of specific gravity 0.5 and chunk of concrete of specific gravity 2.5 are fastened together. The ratio of the mass of wood to the mass of concrete, which makes the combination to float with its entire volume submerged under water is

View answer and explanation

Correct option: C

3 / 5

Option C (3/5) is correct because it represents the ratio of wood mass to concrete mass required for the combination to float fully submerged, based on buoyancy principles.

11 Medium

11 of 390

Understanding +4 | -1

A drop of water breaks into two droplets of equal size. In this process, which of the following statements is correct?

View answer and explanation

Correct option: B

The sum of the masses of the two droplets is equal to mass of drop

Option B (The sum of the masses of the two droplets is equal to mass of drop) is correct because mass is conserved when a drop of water breaks into smaller droplets.

12 Medium

12 of 390

Application +4 | -1

Typical silt(hard mud) particle of radius

20\mathrm{\mu m}

is on the top of lake water, its density is

2000\mathrm{kg}{\mathrm{m}^{ - 3}}

and the viscosity of lake water is 1.0 mPa, density is

1000\mathrm{kg}{\mathrm{m}^{ - 3}}

. If the lake is still(has no internal fluid motion). The terminal speed with which the particle hits the bottom of the lake is ……….

\mathrm{mm}{\mathrm{s}^{ - 1}}

View answer and explanation

Correct option: C

0.87

Option C (0.87) is correct because it is the terminal speed calculated using Stokes' Law, considering the density difference and viscosity.

13 Medium

13 of 390

Application +4 | -1

Consider an iceberg floating in sea water. The density of sea water is

1.03\mathrm{gc}{\mathrm{c}^{ - 1}}

and that ice is

0.92\mathrm{gc}{\mathrm{c}^{ - 1}}

The fraction of total volume of iceberg above the level of sea water is nearby

View answer and explanation

Correct option: D

0.11

Option D (11%) is correct because it is calculated by finding the fraction of the iceberg's volume submerged and then subtracting from 100%.

14 Medium

14 of 390

Understanding +4 | -1

Assertion: The velocity increases, when water flowing in broader pipe enter a narrow pipe.
Reason: According to equation of continuity, product of area and velocity is constant.

View answer and explanation

Correct option: A

If both assertion and reason are true and reason is the correct explanation of the assertion

Option A is correct because both the assertion and reason are true, and the reason correctly explains the assertion based on the equation of continuity.

15 Medium

15 of 390

Application +4 | -1

A tank with a square base of area

1.0\,{{\text{m}}^2}

is divided by a vertical partition in the middle. The bottom of the partition has a small hinzed door of area

20\,{\text{c}}{{\text{m}}^2}.

The tank is filled with water in one compartment and an acid of relative density 1.7 in the other, both to a height of 4m. The force acting on the door is

\left( {g = 1\,{\text{mn}}{{\text{s}}^{ - 2}}} \right)

View answer and explanation

Correct option: B

56 N

Option B (56 N) is correct because the force is calculated by considering the pressure difference due to the different densities of water and acid.

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16 Medium

16 of 390

Application +4 | -1

Water is moving with a speed of

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

through a pipe with a cross-sectional area of

4.20\mathrm{c}{\mathrm{m}^2}

. The water gradually descend 9.66 m as the pipe increase in area to

7.60\mathrm{c}{\mathrm{m}^2}

. The speed of flow at the lower level is

View answer and explanation

Correct option: D

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

Option D (

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

) is correct because it is calculated directly from the equation of continuity,

a_1v_1 = a_2v_2

17 Medium

17 of 390

Application +4 | -1

A trough contains mercury to a depth of 3.6 cm. If some amount of mercury is poured in it then height of mercury in the trough will be

View answer and explanation

Correct option: B

7.2 cm

Option B (7.2 cm) is correct because when the amount of mercury is doubled, the height also doubles.

18 Medium

18 of 390

Understanding +4 | -1

If the temperature of the liquid rises, then its coefficient of viscosity

View answer and explanation

Correct option: B

Decreases

Option B (Decreases) is correct because as temperature rises, the intermolecular forces in a liquid weaken, reducing its viscosity.

19 Medium

19 of 390

Understanding +4 | -1

Two unequal soap bubbles are formed one on each side of a tube closed in the middle by a tap. What happens when the tap is opened to put the two bubbles in communication?

View answer and explanation

Correct option: C

Smaller bubble gradually collapses and the bigger one increases in size

Option C is correct because the smaller bubble has higher pressure, causing air to flow from it to the larger bubble, making the smaller one collapse.

20 Medium

20 of 390

Remembering +4 | -1

Extra pressure inside a soap bubble of radius

r

is proportional to

View answer and explanation

Correct option: D

1 / r

Option D (

\frac{1}{r}

) is correct because the excess pressure inside a soap bubble is inversely proportional to its radius, given by the formula

P = \frac{4T}{r}

, where T is the surface tension.

21 Medium

21 of 390

Analyzing +4 | -1

Statement-1: A block floats in water with some part outside water. When whole system is given a constant upward acceleration then volume of block inside water remains unchanged in equilibrium.
Statement-2: Net force on block in both cases is zero.

View answer and explanation

Correct option: C

Statement-1 is True, Statement-2 is False

Option C is correct. Statement-1 is True because the volume of the block inside water remains unchanged in equilibrium even with constant upward acceleration. Statement-2 is False because the net force on the block is not zero when the system is accelerating upwards.

22 Medium

22 of 390

Understanding +4 | -1

After terminal velocity is reached, the acceleration of a body falling through a fluid is:

View answer and explanation

Correct option: B

Zero

Option B is correct because after terminal velocity is reached, the net force on the body is zero, resulting in zero acceleration.

23 Medium

23 of 390

Analyzing +4 | -1

A: If barometer is accelerated upwards, the level of mercury in the tube of barometer will decrease.
R: The effective value of '

{g}

' increases while the barometer is accelarated up.

View answer and explanation

Correct option: B

Both A and R are true and R is not the correct explanation of A

Option B (Both A and R are true and R is not the correct explanation of A) is correct because both the assertion and the reason are true, but the reason does not explain the assertion.

24 Medium

24 of 390

Application +4 | -1

The terminal velocity

({v_t})

of the spherical rain drop depends on the radius

(r)

of the spherical rain drop as

View answer and explanation

Correct option: C

{r^2}

Option C (

{r^2}

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

25 Medium

25 of 390

Understanding +4 | -1

If a cube of ice is placed in gravity free space,
then when the ice melts.

View answer and explanation

Correct option: D

It will form a spherical shape

Option D (It will form a spherical shape) is correct because in the absence of gravity, surface tension will minimize the surface area, resulting in a spherical shape.

26 Medium

26 of 390

Understanding +4 | -1

Statement – 1: It is difficult to stop bleeding from a cut in the body at high altitude
Statement – 2: The atmospheric pressure at high altitude is lesser than the blood pressure.

View answer and explanation

Correct option: A

Statement – 1 is true, Statement – 2 is true; Statement – 2 is a correct explanation for Statement – 1

Option A is correct because the lower atmospheric pressure at high altitudes reduces the external pressure on blood vessels, making it harder to stop bleeding.

27 Medium

27 of 390

Understanding +4 | -1

Assertion: Bernoulli's equation holds for non-steady or turbulent flows.
Reason: In these situations, velocity and pressure are constant with time.

View answer and explanation

Correct option: D

If both assertion and reason are false

Option D is correct because Bernoulli's equation is only applicable to steady, incompressible, and non-viscous flows, where velocity and pressure are not constant with time in turbulent flows.

28 Medium

28 of 390

Application +4 | -1

A fully loaded Boeing aircraft 747 has a mass of

33 \times 10^5 \mathrm{~kg}

. Its total wing area is

500 \mathrm{~m}^2

. It is in level flight with a speed of

960 \mathrm{~km} / \mathrm{h}

. (a) Estimate the pressure difference between the lower and upper surfaces of the wings. (b) Estimate the fractional increase in the speed of the air on the upper surface of the wing relative to the lower surface. The density of air is

\rho=1.2 \mathrm{~kg} \mathrm{~m}^{-3}

and

g=9.81 \mathrm{~ms}^{-2}

View answer and explanation

Correct option: A

6.5 \times 10^3 \mathrm{~Nm}^{-2}; 8 \%

Option D (

1.95 \mathrm{~V}

) is correct because it is the potential difference calculated using Ohm's law, considering the internal resistance of the cell.

29 Medium

29 of 390

Application +4 | -1

A liquid drop of radius

r

and surface tension

T

is split into 125 drops of equal size work done in this process is

View answer and explanation

Correct option: B

16\pi {r^2}T

Option B (

16\pi {r^2}T

) is correct because it calculates the work done by finding the difference in surface area before and after splitting the drop.

30 Medium

30 of 390

Application +4 | -1

A horizontal pipe of cross-sectional diameter 4 cm carries water at a speed of 6 m/s. The pipe is connected to a smaller pipe with a cross-sectional diameter 2 cm. The velocity of the water through the smaller pipe is

View answer and explanation

Correct option: D

24 m/s

Option D (24 m/s) is correct because the velocity is calculated using the principle of continuity, where the product of area and velocity remains constant.

Revision notes and key takeaways

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Key Takeaways

✓ This set contains 390 single-correct-answer MCQs on MECHANICAL PROPERTIES OF FLUIDS.
✓ Try each question before opening its answer. Read the explanation where one is available.
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