Fluid Mechanics PYQs Set 3 (PDF)

Set 3 of 8 · Questions 61-90 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Fluid Mechanics · Set 3 (Q61-90)
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61. $Assume that a drop of liquid evaporates by decreasing in its surface energy, so that its temperature remains unchanged. What should be the minimum radius of the drop for this to be possible? The surface tension is T, density of liquid is ρ and L is its latent heat of vaporization.$ (1) $ρL/T$ (2) $T / ρL$ (3) $T/ρL$ (4) $2T/ρL$ 62. $Two solid pieces, one of steel and the other of aluminium when immersed completely in water have equal weights. When the solid pieces are weighed in air$ (1) $the weight of aluminium is half the weight of steel$ (2) $steel piece will weigh more$ (3) $they have the same weight$ (4) $aluminium piece will weigh more.$ 63. $A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5\times 1 0^{-2} N/m. The pressure inside the bubble equals at a point Z_{0} below the free surface of water in a container. Taking g = 10 m/ s^{2}, density of water = 1 0^{3} kg/ m^{3}, the value of Z_{0} is:$ (1) $0.5 cm$ (2) $100 cm$ (3) $10 cm$ (4) $1 cm$ 64. $Two capillary tubes P and Q are dipped vertically in water. The height of water level in capillary tube P is (\frac{2}{3})^{rd} of the height in capillary tube Q . The ratio of their diameter is$ (1) $2 : 3$ (2) $3 : 2$ (3) $3 : 4$ (4) $4 : 3$ 65. $If a soap bubble expands, the pressure inside the bubble [NEET 2022]$ (1) $increases$ (2) $remains the same$ (3) $is equal to the atmospheric pressure$ (4) $decreases$ 66. $The specific heat of water = 4200 Jkg^{- 1} K^{- 1} and the latent heat of ice = 3.4 \times 10^{5} Jkg^{- 1} 100 grams of ice at 0^{\circ} C is placed in 200 g of water at 25^{\circ} C . The amount of ice that will melt as the temperature of water reaches 0^{\circ} C is close to (in grams)$ (1) $69.3$ (2) $63.8$ (3) $64.6$ (4) $61.7$ 67. $A spherical drop of radium r is divided in to 8 equal droplets. If the surface tension is S, then the work done in the process will be$ (1) $2 π r^{2} S$ (2) $3 π r^{2} S$ (3) $4 π r^{2} S$ (4) $4 π r^{2} S^{2}$ 68. $The angle of contact is 120^{\circ} when a cylindrical rod is vertically placed in a liquid. If the same rod is placed horizontally in the liquid, then the angle of contact is$ (1) $60^{\circ}$ (2) $30^{\circ}$ (3) $90^{\circ}$ (4) $120^{\circ}$ 69. $A rectangular film of liquid is extended from (4 cm \times 2cm) to (5 cm \times 4 cm). If the work done is 3 \times 1 0^{-4} J, the value of the surface tension of the liquid i$ (1) $8.0 N m^{-1}$ (2) $0.250 N m^{-1}$ (3) $0.125 N m^{-1}$ (4) $0.2 N m^{-1}$ 70. $A barometer is constructed using a liquid (density = 760 kg / m^{3}). What would be the height of the liquid column, when a mercury barometer reads 76 cm? (Density of mercury = 13600 kg / m^{3}) [NEET 2020]$ (1) $1.36 m$ (2) $13.6 m$ (3) $136 m$ (4) $0.76 m$ 71. $Correct Bernoulli's equation is (symbols have their usual meaning):$ (1) $P + m g h + \frac{1}{2} m v^{2} = constant$ (2) $P + ρ g h + \frac{1}{2} ρ v^{2} = constant$ (3) $P + ρ g h + ρ v^{2} = constant$ (4) $P + \frac{1}{2} ρ g h + \frac{1}{2} ρ v^{2} = constant$ 72. $A shower head has 25 circular openings, each with radius 1 mm . The shower head is connected to a pipe with radius 2 cm . If the speed of the water in the pipe is 25 cm / s . What is its speed as it exists the shower head openings?$ (1) $1 m / s$ (2) $2 m / s$ (3) $4 m / s$ (4) $5 m / s$ 73. $A body is suspended by a light string. The tensions in the string when the body is in air, when the body is totally immersed in water and when the body is totally immersed in a liquid are respectively 40.2 N, 28.4 N and 16.6 N . The density of the liquid is$ (1) $1200 kg - m^{- 3}$ (2) $1600 kg^{- m^{- 3}}$ (3) $2000 kg - m^{- 3}$ (4) $2400 kg - m^{- 3}$ 74. $The amount of work done to break a big water drop of radius ' R' into 27 small drops of equal radius is 10 J. The work done required to break the same big drop into 64 small drops of equal radius will be$ (1) $15 J$ (2) $5 J$ (3) $20 J$ (4) $10 J$ 75. $Consider an increase of 1 % in each of radius of artery, viscosity of blood and density of blood respectively. The percentage change in flow rate of blood in artery is$ (1) $0.25 %$ (2) $0.50 %$ (3) $1.0 %$ (4) $3.0 %$ 76. $The speed of the water in a river is v near the surface. If the coefficient of viscosity of water is η and the depth of the river is H, then the shearing stress between the horizontal layers of water is$ (1) $η \frac{H}{v}$ (2) $η \frac{v}{H}$ (3) $\frac{v}{η H}$ (4) $η ν H$ 77. $1000 spherical drops of water each 10^{- 8} m in diameter coalesce to form one large spherical drop. The amount of energy liberated in this process (in joule) is (surface tension of water is 0.075 N / m).$ (1) $10.75 π \times 10^{- 15}$ (2) $6.75 π \times 10^{- 15}$ (3) $8.65 π \times 10^{- 15}$ (4) $3.88 π \times 10^{- 15}$ 78. $A person of height 1.65 m is standing upright. The additional external force required by 'blood vessel of length 1 cm, diameter 1 mm at feet to balance the pressure compared to similar blood vessel in head is (Density of blood = 1.1 \times 10^{3} kg m^{- 3}, g = 10 ms^{- 2})$ (1) $0.57 N$ (2) $5.7 N$ (3) $1.85 N$ (4) $3.14 N$ 79. $Three liquids of equal masses are taken in three identical cubical vessels A, B and C . Their densities are ρ_{A}, ρ_{B} and ρ_{C} respectively. But ρ_{A} < ρ_{B} < ρ_{C} . The force exerted by the liquid on the base of the cubical vessel is$ (1) $maximum in vessel C$ (2) $minimum in vessel C$ (3) $the same in all the vessels$ (4) $maximum in vessel A .$ 80. $Pressure inside a soap bubble is greater than the pressure outside by an amount: (given: R = Radius of bubble S = Surface tension of bubble)$ (1) $\frac{2 S}{R}$ (2) $\frac{4 R}{S}$ (3) $\frac{S}{R}$ (4) $\frac{4 S}{R}$ 81. $A water drop of radius 1cm is broken into 729 equal droplets. If surface tension of water is 75 dyne/cm, then the gain in surface energy upto first decimal place will be: [Given π = 3.14]$ (1) $8. 5 x 1 0^{- 4} J$ (2) $8. 2 x 1 0^{- 4} J$ (3) $7. 5 x 1 0^{- 4} J$ (4) $5. 3 x 1 0^{- 4} J$ 82. $The top of a water tank is open to air and its water level is maintained. It is giving out 0.74 m^{3} water per minute through a circular opening of 2 cm radius in its wall. The depth of the centre of the opening from the level of water in the tank is close to:$ (1) $6.0 m$ (2) $4.8 m$ (3) $9.6 m$ (4) $2.9$ 83. $A solid metal sphere released in a vertical liquid column has attained terminal velocity in the downward direction. The magnitudes of viscous force, buoyant force and gravitational force acting on it are F_{v}, F_{B} and F_{W} respectively. Then the correct relation between them is$ (1) $F_{B} > F_{V} = F_{W}$ (2) $F_{w} = F_{V} + F_{B}$ (3) $F_{B} = F_{W} + F_{V}$ (4) $F_{V} = F_{B} + F_{W}$ 84. $If there were no gravity, which of the following will not be there for a fluid?$ (1) $Viscosity$ (2) $Surface tension$ (3) $Pressure$ (4) $Archimedes's upward thrust$ 85. $A rectangular vessel when full of water, takes 10 minutes to be emptied through an orifice in its bottom. How much time will it take to be emptied when half filled with water?$ (1) $9 minutes$ (2) $7 minutes$ (3) $5 minutes$ (4) $3 minutes$ 86. $What is the rate at which a trapped bubble of 2 mm diameter rises slightly through a solution of density 13.6 \times 10^{3} kg / m^{3} and coefficient of viscosity 1.5 centipoise? Assume, the density of air is negligibility and g = 10 m / s^{2} .$ (1) $20 m / s$ (2) $2 m / s$ (3) $0.2 m / s$ (4) $0.02 m / s$ 87. $A cubical block of density ρ_{b} = 600 kg / m^{3} floats in a liquid of density ρ_{e} = 900 kg / m^{3} . If the height of block is H = 8.0 cm then height of the submerged part is____cm.$ (1) $6.3$ (2) $4.3$ (3) $5.3$ (4) $7.3$ 88. $A cube of metal is subjected to a hydrostatic pressure of 4 GPa . The percentage change in the length of the side of the cube is close to (Given bulk modulus of metal, B = 8 \times 10^{10} Pa)$ (1) $0.6$ (2) $20$ (3) $1.67$ (4) $5$ 89. $A capillary tube of radius 0.1 mm is dipped in water. The water rises to a height of 2 cm in the tube. If the surface tension of water is 0.072 Nm^{- 1}, the contact angle between water and wall of the tube is$ (1) $θ = cos^{- 1} (\frac{1}{3.6})$ (2) $θ = cos^{- 1} (\frac{1}{7.2})$ (3) $θ = cos^{- 1} (\frac{1}{1.8})$ (4) $θ = cos^{- 1} (\frac{1}{6.2})$ 90. $A 0.5 kg block of brass (density = 8 \times 10^{3} kg m^{- 3}) is suspended from a string. What is the tension in the string if the block is completely immersed in water? (g = 10 ms^{- 2})$ (1) $5 N$ (2) $\frac{0.5}{8 \times 10 ^{3}} N$ (3) $\frac{5}{8} N$ (4) $\frac{35}{8} N$