JEE Physics Mechanical Properties Of Fluids MCQs Set 07

Physics Objective Questions and Answers: Mechanical Properties Of Fluids

Review structured MCQ sets for JEE Physics Mechanical Properties Of Fluids. Built according to official JEE guidelines, these downloadable questions support daily revision and core concept reinforcement.

Download Mechanical Properties Of Fluids MCQs with Answers

Access the complete set of multiple-choice questions for Mechanical Properties Of Fluids below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official JEE textbooks.

Multiple Choice Questions

Question 1: The velocity of a falling raindrop attains a limiting value because of:
(a) surface tension
(b) upthrust due to air
(c) viscous force exerted by air
(d) air current
Show Answer & Explanation

Answer: (c) viscous force exerted by air

Explanation:
1. As speed increases the viscous drag increases until it balances the net downward force

Teacher's Note:
1. Apply the standard formula and check the units.

Question 2:
Assertion (A): Machine parts are jammed in winter.
Reason (R): The viscosity of the lubricant used in machine parts decreases at low temperature.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. A lubricant becomes more viscous in the cold, so parts jam and A is true
2. R says viscosity decreases, which is false

Teacher's Note:
1. Decide whether each statement is true, then whether R explains A.

Question 3: Poise is the unit of:
(a) pressure
(b) friction
(c) surface tension
(d) viscosity
Show Answer & Explanation

Answer: (d) viscosity

Explanation:
1. 1 poise = 0.1 N s/m2, the CGS unit of viscosity

Teacher's Note:
1. Apply the standard formula and check the units.

Question 4: Two raindrops falling through air have radii in the ratio 1 : 2. They will have terminal velocities in the ratio:
(a) 4 : 1
(b) 1 : 4
(c) 2 : 1
(d) 1 : 2
Show Answer & Explanation

Answer: (b) 1 : 4

Explanation:
1. Terminal velocity is proportional to r^2, so 1 : 4

Teacher's Note:
1. Apply the standard formula and check the units.

Question 5: A sphere of mass M and radius R is falling in a viscous fluid. The terminal velocity attained by the falling object will be proportional to (neglecting buoyancy):
(a) \( MR^2 \)
(b) \( M/R \)
(c) \( MR \)
(d) \( M/R^2 \)
Show Answer & Explanation

Answer: (b) \( M/R \)

Explanation:
1. Terminal velocity = M g/(6 pi eta R)

Teacher's Note:
1. Apply the standard formula and check the units.

Question 6: A drop of water of radius 0.0015 mm is falling in air. The coefficient of viscosity of air is \( 2.0\times10^{-5} \) kg/(m s). The terminal velocity of the drop is (density of water = 1000 kg/m3, g = 10 m/s2):
(a) \( 1.0\times10^{-4} \) m/s
(b) \( 2.0\times10^{-4} \) m/s
(c) \( 2.5\times10^{-4} \) m/s
(d) \( 5.0\times10^{-4} \) m/s
Show Answer & Explanation

Answer: (c) \( 2.5\times10^{-4} \) m/s

Explanation:
1. v = 2 r^2 rho g/(9 eta) = 2 x (1.5e-6)^2 x 1000 x 10/(9 x 2e-5)
2. = 4.5e-8/1.8e-4 = 2.5e-4 m/s

Teacher's Note:
1. Apply the standard formula and check the units.

Question 7:
Assertion (A): For Reynolds number Re greater than 2000, the flow of a fluid is turbulent.
Reason (R): Inertial forces are dominant compared to viscous forces at such high Reynolds numbers.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Re is the ratio of inertial to viscous forces
2. Large inertial effects produce turbulence

Teacher's Note:
1. Decide whether each statement is true, then whether R explains A.

Question 8: Spiders and insects move on the surface of water without sinking because:
(a) an elastic membrane is formed on water due to surface tension
(b) spiders and insects are light
(c) spiders and insects swim on water
(d) spiders and insects experience upthrust
Show Answer & Explanation

Answer: (a) an elastic membrane is formed on water due to surface tension

Explanation:
1. Surface tension acts like an elastic skin that supports their weight

Teacher's Note:
1. Apply the standard formula and check the units.

Question 9: A thin liquid film is formed between a U-shaped wire and a light slider that supports a weight of \( 1.5\times10^{-2} \) N. The length of the slider is 30 cm. The surface tension of the film is:
(a) 0.025 N/m
(b) 0.0125 N/m
(c) 0.1 N/m
(d) 0.05 N/m
Show Answer & Explanation

Answer: (a) 0.025 N/m

Explanation:
1. The film has two surfaces, so 2 T l = W
2. T = 1.5e-2/(2 x 0.3) = 0.025 N/m

Teacher's Note:
1. Apply the standard formula and check the units.

Question 10: A liquid drop of diameter D breaks into 27 tiny drops. The resultant change in energy is:
(a) \( 2\pi TD^2 \)
(b) \( 4\pi TD^2 \)
(c) \( \pi TD^2 \)
(d) none of these
Show Answer & Explanation

Answer: (a) \( 2\pi TD^2 \)

Explanation:
1. Each small drop has diameter D/3
2. Area of 27 drops = 27 pi D^2/9 = 3 pi D^2
3. Change = T(3 pi D^2 - pi D^2) = 2 pi T D^2

Teacher's Note:
1. Apply the standard formula and check the units.

Question 11: The excess pressure inside an air bubble of radius r just below the surface of water is p1. The excess pressure inside a drop of the same radius just outside the surface is p2. If T is the surface tension, then:
(a) \( p_1=2p_2 \)
(b) \( p_1=p_2 \)
(c) \( p_2=2p_1 \)
(d) \( p_2=0,\ p_1\ne0 \)
Show Answer & Explanation

Answer: (b) \( p_1=p_2 \)

Explanation:
1. An air bubble in water has one surface, so p1 = 2T/r
2. A liquid drop in air also has one surface, so p2 = 2T/r

Teacher's Note:
1. Apply the standard formula and check the units.

Question 12:
Assertion (A): Turbulence is always dissipative.
Reason (R): A high Reynolds number promotes turbulence.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Turbulence converts kinetic energy to heat, so A is true
2. A high Reynolds number does promote turbulence, but that does not explain why it is dissipative

Teacher's Note:
1. Decide whether each statement is true, then whether R explains A.

Question 13: A water drop is divided into 8 equal droplets. The pressure difference between the inner and outer sides of the big drop:
(a) will be the same as for a smaller droplet
(b) will be half of that for a smaller droplet
(c) will be one-fourth of that for a smaller droplet
(d) will be twice that for a smaller droplet
Show Answer & Explanation

Answer: (b) will be half of that for a smaller droplet

Explanation:
1. Radius of a droplet is half that of the big drop
2. Excess pressure 2T/r is inversely proportional to r, so the big drop has half

Teacher's Note:
1. Apply the standard formula and check the units.

Question 14: A false statement is:
(a) angle of contact is less than 90 degrees if cohesive force is less than adhesive force x sqrt2
(b) angle of contact is greater than 90 degrees if cohesive force is greater than adhesive force x sqrt2
(c) angle of contact is 90 degrees if cohesive force equals adhesive force x sqrt2
(d) if the radius of the capillary is reduced to half, the rise of liquid column becomes four times
Show Answer & Explanation

Answer: (d) if the radius of the capillary is reduced to half, the rise of liquid column becomes four times

Explanation:
1. Rise h is proportional to 1/r, so halving the radius doubles the height, not four times

Teacher's Note:
1. Apply the standard formula and check the units.

Question 15: If a capillary of radius r is dipped in water, the height of water that rises in it is h and its mass is M. If the radius of the capillary is doubled, the mass of water that rises in the capillary will be:
(a) 4M
(b) 2M
(c) M
(d) M/2
Show Answer & Explanation

Answer: (b) 2M

Explanation:
1. h is proportional to 1/r and the volume is proportional to r^2 h
2. So mass is proportional to r and doubles

Teacher's Note:
1. Apply the standard formula and check the units.

Question 16: A capillary of radius r dipped in water has water rising to height H, and the potential energy of the water is u1. If a capillary of radius 2r is dipped in water, the potential energy is u2. The ratio u1/u2 is:
(a) 2 : 1
(b) 1 : 2
(c) 4 : 1
(d) 1 : 1
Show Answer & Explanation

Answer: (d) 1 : 1

Explanation:
1. Mass raised is proportional to r and the height of its centre is proportional to 1/r, so u = (m g h/2) is the same in both

Teacher's Note:
1. Apply the standard formula and check the units.

Question 17:
Assertion (A): The angle of contact of a liquid decreases with an increase in temperature.
Reason (R): With an increase in temperature, the surface tension of the liquid increases.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. Surface tension falls as temperature rises, so cos(theta) rises and the angle decreases, so A is true
2. R is false

Teacher's Note:
1. Decide whether each statement is true, then whether R explains A.

Question 18: A vessel whose bottom has round holes of diameter 0.1 mm is filled with water. The maximum height to which water can be filled without leakage is (S.T. of water = 75 dyne/cm, g = 1000 cm/s2):
(a) 100 cm
(b) 75 cm
(c) 50 cm
(d) 30 cm
Show Answer & Explanation

Answer: (d) 30 cm

Explanation:
1. h = 2T/(r rho g) = 2 x 75/(0.005 x 1 x 1000) = 30 cm

Teacher's Note:
1. Apply the standard formula and check the units.

Question 19: In a surface tension experiment, water rises up to 0.1 m in a capillary tube. If the same experiment is done in an artificial satellite revolving round the earth, water will rise in the capillary tube up to a height of:
(a) 0.1 m
(b) 0.98 m
(c) 9.8 m
(d) the full length of the capillary tube
Show Answer & Explanation

Answer: (d) the full length of the capillary tube

Explanation:
1. In a satellite the effective g is zero, so there is no weight to balance and the liquid fills the tube

Teacher's Note:
1. Apply the standard formula and check the units.

Question 20: A soap bubble of radius 3 cm in vacuum and another of radius 4 cm in vacuum coalesce under isothermal conditions. The radius of the new bubble is:
(a) 2.3 cm
(b) 4.5 cm
(c) 5 cm
(d) 7 cm
Show Answer & Explanation

Answer: (c) 5 cm

Explanation:
1. In vacuum there is no outside pressure, so total surface area adds in effect: R^2 = r1^2 + r2^2 = 9 + 16
2. R = 5 cm

Teacher's Note:
1. Apply the standard formula and check the units.

Question 21: The spherical shape of a rain drop is due to:
(a) density of the liquid
(b) surface tension
(c) atmospheric pressure
(d) gravity
Show Answer & Explanation

Answer: (b) surface tension

Explanation:
1. Surface tension minimises surface area, which for a given volume gives a sphere

Teacher's Note:
1. Apply the standard formula and check the units.

Question 22:
Assertion (A): A needle placed carefully on the surface of water may float.
Reason (R): It may float due to surface tension, as the upward forces due to surface tension balance the weight of the needle.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. The film is depressed and supports the needle through the vertical component of surface tension
2. R explains A

Teacher's Note:
1. Decide whether each statement is true, then whether R explains A.

Question 23: In a capillary tube, water rises by 1.2 mm. The height of water that will rise in another capillary tube having half the radius of the first is:
(a) 1.2 mm
(b) 2.4 mm
(c) 0.6 mm
(d) 0.4 mm
Show Answer & Explanation

Answer: (b) 2.4 mm

Explanation:
1. h is proportional to 1/r, so half the radius gives double the height, 2.4 mm

Teacher's Note:
1. Apply the standard formula and check the units.

Question 24: Water rises to a height h in a capillary at the surface of the earth. On the surface of the moon the height of the water column in the same capillary will be:
(a) 6h
(b) h/6
(c) h
(d) zero
Show Answer & Explanation

Answer: (a) 6h

Explanation:
1. h is proportional to 1/g
2. g on the moon is about g/6, so the height is 6h

Teacher's Note:
1. Apply the standard formula and check the units.

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