Mechanical Properties of Fluids

20 JEE Main questions · Physics

Surface tension

PhysicsJEE Main 21 Jan 2026, Shift 2·Q13·MCQ·Easy–moderate
Open
Surface tension of two liquids (having same densities), $T_1$ and $T_2$ , are measured using capillary rise method utilizing two tubes with inner radii of $r_1$ and $r_2$ where $r_1 > r_2$ . The measured liquid heights in these tubes are $h_1$ and $h_2$ respectively. [Ignore the weight of the liquid above the lowest point of meniscus]. The heights $h_1$ and $h_2$ and surface tensions $T_1$ and $T_2$ satisfy the relation :
1. (1) $h_1 < h_2$ and $T_1 = T_2$
2. (2) $h_1 = h_2$ and $T_1 = T_2$
3. (3) $h_1 > h_2$ and $T_1 = T_2$
4. (4) $h_1 > h_2$ and $T_1 < T_2$
We corrected a printing error in the original paper
Source printed “about the lowest point of miniscus”.
PhysicsJEE Main 22 Jan 2026, Shift 1·Q8·MCQ·Easy
Open
Given below are two statements:
Statement I: Pressure of fluid is exerted only on a solid surface in contact as the fluid-pressure does not exist everywhere in a still fluid.
Statement II: Excess potential energy of the molecules on the surface of a liquid, when compared to interior, results in surface tension.
In the light of the above statements, choose the correct answer from the options given below.
1. (1)Statement I is true but Statement II is false
2. (2)Both Statement I and Statement II are false
3. (3)Both Statement I and Statement II are true
4. (4)Statement I is false but Statement II is true
PhysicsJEE Main 22 Jan 2026, Shift 2·Q9·MCQ·Easy–moderate
Open
When a part of a straight capillary tube is placed vertically in a liquid, the liquid rises upto certain height h. If the inner radius of the capillary tube, density of the liquid and surface tension of the liquid decrease by 1 % each, then the height of the liquid in the tube will change by %.
1. (1) $-1$
2. (2) $+3$
3. (3) $-3$
4. (4) $+1$
We corrected a printing error in the original paper
Source printed “the liquid raises upto certain height”.
PhysicsJEE Main 24 Jan 2026, Shift 2·Q25·Numerical·Easy–moderate
Open
A soap bubble of surface tension 0.04 N/m is blown to a diameter of 7 cm. If $(15000 - x)\ \mu$ J of work is done in blowing it further to make its diameter 14 cm, then the value of $x$ is .
( $\pi = 22/7$ )
PhysicsJEE Main 2 Apr 2026, Shift 1·Q20·MCQ·Easy–moderate
Open
A liquid drop of diameter 2 mm breaks into 512 droplets. The change in surface energy is $\alpha\times10^{-6}$ J. The value of $\alpha$ is . (Take surface tension of liquid $= 0.08$ N/m)
1. (1)10
2. (2)7
3. (3)8
4. (4)11
PhysicsJEE Main 2 Apr 2026, Shift 2·Q8·MCQ·Easy–moderate
Open
The surface tension of a soap bubble is 0.03 N/m. The work done in increasing the diameter of bubble from 2 cm to 6 cm is $\alpha\pi\times10^{-4}$ J. The value of $\alpha$ is . (Take $\pi = 3.14$ )
1. (1)0.86
2. (2)0.64
3. (3)1.92
4. (4)7.68
PhysicsJEE Main 4 Apr 2026, Shift 1·Q22·Numerical·Easy–moderate
Open
The surface tension of a soap solution is $3.5\times10^{-2}$ N/m. The work required to increase the radius of a soap bubble from 1 cm to 2 cm is $\alpha\times10^{-6}$ J. The value of $\alpha$ is . ( $\pi = 22/7$ )
PhysicsJEE Main 5 Apr 2026, Shift 2·Q8·MCQ·Easy–moderate
Open
Eight mercury drops, each of radius $r$ , coalesce to form a bigger drop. The surface energy released in this process is. ( $S$ is the surface tension of mercury).
1. (1) $8\pi r^2S$
2. (2) $16\pi r^2S$
3. (3) $64\pi r^2S$
4. (4) $4\pi r^2S$

Viscosity

PhysicsJEE Main 21 Jan 2026, Shift 2·Q22·Numerical·Easy–moderate
Open
The terminal velocity of a metallic ball of radius 6 mm in a viscous fluid is 20 cm/s. The terminal velocity of another ball of same material and having radius 3 mm in the same fluid will be cm/s.
PhysicsJEE Main 23 Jan 2026, Shift 2·Q20·MCQ·Easy–moderate
Open
A small metallic sphere of diameter 2 mm and density $10.5\ \mathrm{g/cm^3}$ is dropped in glycerine having viscosity 10 Poise and density $1.5\ \mathrm{g/cm^3}$ respectively. The terminal velocity attained by the sphere is cm/s.
( $\pi = \dfrac{22}{7}$ and $g = 10\ \mathrm{m/s^2}$ )
1. (1)2.0
2. (2)1.0
3. (3)3.0
4. (4)1.5
PhysicsJEE Main 24 Jan 2026, Shift 1·Q25·Numerical·Easy–moderate
Open
Sixty four rain drops of radius 1 mm each falling down with a terminal velocity of 10 cm/s coalesce to form a bigger drop. The terminal velocity of bigger drop is cm/s.
PhysicsJEE Main 2 Apr 2026, Shift 2·Q10·MCQ·Easy–moderate
Open
If an air bubble of diameter 2 mm rises steadily through a liquid of density $2000\ \mathrm{kg/m^3}$ at a rate of 0.5 cm/s, then the coefficient of viscosity of liquid is Poise. (Take $g = 10\ \mathrm{m/s^2}$ )
1. (1)0.88
2. (2)8.8
3. (3)88.8
4. (4)0.088
PhysicsJEE Main 8 Apr 2026, Shift 2·Q9·MCQ·Easy–moderate
Open
A spherical liquid drop of radius $R$ acquires the terminal velocity $v_1$ when it falls through a gas of viscosity $\eta$ . Now the drop is broken into 64 identical droplets and each droplet acquires terminal velocity $v_2$ falling through the same gas. The ratio of terminal velocities $v_1/v_2$ is .
1. (1)4
2. (2)0.25
3. (3)32
4. (4)16
We corrected a printing error in the original paper
Source printed “when falls through a gas”.

Fluid dynamics

PhysicsJEE Main 21 Jan 2026, Shift 1·Q4·MCQ·Moderate
Open
Water flows through a horizontal tube as shown in the figure. The difference in height between the water columns in vertical tubes is 5 cm and the areas of cross-sections at $A$ and $B$ are $6\ \mathrm{cm^2}$ and $3\ \mathrm{cm^2}$ respectively. The rate of flow will be $\mathrm{cm^3/s}$ . (take $g = 10\ \mathrm{m/s^2}$ )
1. (1) $\dfrac{200}{\sqrt3}$
2. (2) $200\sqrt6$
3. (3) $200\sqrt3$
4. (4) $100\sqrt3$
We corrected a printing error in the original paper
Source printed “the area of cross-sections at $A$ and $B$ are”.
PhysicsJEE Main 4 Apr 2026, Shift 2·Q7·MCQ·Easy–moderate
Open
A water spray gun is attached to a hose of cross sectional area $30\ \mathrm{cm^2}$ . The gun comprises of 10 perforations each of cross sectional area of $15\ \mathrm{mm^2}$ . If the water flows in the hose with the speed of 50 cm/s, calculate the speed at which the water flows out from each perforation. (Neglect any edge effects)
1. (1)100 m/s
2. (2)10 m/s
3. (3)1000 m/s
4. (4) $15\times10^{2}$ m/s
PhysicsJEE Main 6 Apr 2026, Shift 2·Q9·MCQ·Moderate
Open
A cylindrical vessel of 40 cm radius is completely filled with water and its capacity is 528 $\mathrm{dm^3}$ (dm : decimeter). The vessel is placed on a solid block of exactly same height as vessel. If a small hole is made at 70 cm below the top of water level, then horizontal range of water falling on the ground in the beginning is cm.
1. (1) $120\sqrt2$
2. (2) $140\sqrt2$
3. (3) $140\sqrt3$
4. (4) $120\sqrt3$
PhysicsJEE Main 8 Apr 2026, Shift 2·Q8·MCQ·Easy–moderate
Open
A liquid of density $600\ \mathrm{kg/m^3}$ is flowing steadily in a tube of varying cross-section. The cross-section at a point A is $1.0\ \mathrm{cm^2}$ and that at B is $20\ \mathrm{mm^2}$ . Both the points A and B are in same horizontal plane, the speed of the liquid at A is 10 cm/s. The difference in pressures at A and B points is Pa.
1. (1)18
2. (2)144
3. (3)36
4. (4)72
We corrected a printing error in the original paper
Source printed “A liquid of density 600 kg/m $^3$ flowing steadily” (verb missing); “The difference is pressures”.

Fluid statics

PhysicsJEE Main 22 Jan 2026, Shift 1·Q12·MCQ·Tough
Open
A cylindrical tube $AB$ of length $l$ , closed at both ends contains an ideal gas of 1 mol having molecular weight $M$ . The tube is rotated in a horizontal plane with constant angular velocity $\omega$ about an axis perpendicular to $AB$ and passing through the edge at end A, as shown in the figure. If $P_A$ and $P_B$ are the pressures at $A$ and $B$ respectively, then (Consider the temperature is same at all points in the tube)
1. (1) $P_B = P_A\exp\left(M\omega^2l^2/2RT\right)$
2. (2) $P_B = P_A$
3. (3) $P_B = P_A\exp\left(M\omega^2l^2/3RT\right)$
4. (4) $P_B = P_A\exp\left(M\omega^2l^2/RT\right)$
PhysicsJEE Main 24 Jan 2026, Shift 2·Q12·MCQ·Easy–moderate
Open
A cubical block of density $\rho_b = 600\ \mathrm{kg/m^3}$ floats in a liquid of density $\rho_e = 900\ \mathrm{kg/m^3}$ . If the height of block is $H = 8.0$ cm then height of the submerged part is cm.
1. (1)7.3
2. (2)4.3
3. (3)6.3
4. (4)5.3
PhysicsJEE Main 2 Apr 2026, Shift 1·Q25·Numerical·Easy–moderate
Open
A tube is filled with water and a wooden cube $10\ \mathrm{cm}\times10\ \mathrm{cm}\times10\ \mathrm{cm}$ is placed in the water. The wooden cube is found to float on the water with a part of it submerged in water. When a metal coin is placed on the wooden cube, the submerged part is increased by 3.87 cm. The mass of the metal coin is gram. (Take water density as $1\ \mathrm{g/cm^3}$ and density of wood as $0.4\ \mathrm{g/cm^3}$ )