CBSE Class 11 Physics Mechanical Properties of Fluids MCQs Set 03

Question: Two non-mixing liquids of densities r and nr (n > 1) are put in a container. The height of each liquid is h. A solid cylinder of length L and density d is put in this container. The cylinder floats with its axis vertical and length pL (p < 1) in the denser liquid. The density d is equal to
a) {2 + (n – 1)p}r
b) {1 + (n – 1)p}r
c) {1 + (n + 1)p}r
d) {2 + (n + 1)p}r
Answer: b

Question: A small hole of area of cross-section 2 mm2 is present near the bottom of a fully filled open tank of height 2 m. Taking g = 10 m/s², the rate of flow of water through the open hole would be nearly
a) 6.4 × 10^–6 m³/s
b) 12.6 × 10^–6 m³/s
c) 8.9 × 10^–6 m³/s
d) 2.23 × 10^–6 m³/s
Answer: b

Question: The angle of contact at the interface of waterglass is 0°, Ethylalcohol-glass is 0°, mercuryglass is 140° and Methyliodide-glass is 30°. A glass capillary is put in a trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the trough is
a) water
b) ethylalcohol
c) mercury
d) methyliodide.
Answer: c

Question: Water is flowing in a river. If the velocity of a layer at a distance 10 cm from the bottom is 20 cm/s, the velocity of layer at a height of 40 cm from the bottom is
a) 10 cm/s
b) 20 cm/s
c) 30 cm/s
d) 80 cm/s
Answer: d

Question: A liquid is contained in a vessel. The liquid-solid adhesive force is very weak as compared to the cohesive force in the liquid. The shape of the liquid surface will be
a) horizontal
b) vertical
c) concave
d) convex
Answer: d

Question: Toricelli’s theorem is used to find
a) the velocity of efflux through an orifice.
b) the velocity of flow of liquid through a pipe.
c) terminal velocity
d) critical velocity
Answer: a 

Question: Gases do not posses
a) density
b) surface tension
c) volume
d) viscosity
Answer: b

Question: The terminal speed of a sphere of gold (density = 19.5 kg m^–3) is 0.2 m s^–1 in a viscous liquid (density = 1.5 kg m^–3). Then the terminal speed of a sphere of silver (density = 10.5 kg m^–3) of the same size in the same liquid is
a) 0.1 m s^–1
b) 0.4 m s^–1
c) 0.2 m s^–1
d) 0.3 m s^–1
Answer: a

Question: Which of the following diagrams does not represent a streamline flow?

Answer: d

Question: The rate of flow of a liquid through a capillary tube of radius r is V when the pressure difference across the two ends of the capillary is P. If pressure is increased by 3P and radius is reduced to r/2 , then the rate of flow becomes
a) V/8
b) V/4
c) V/2
d) V/9
Answer: b

Question: An aircraft of mass 4 × 10⁵ kg with total wing area 500 m² in level flight at a speed of 720 km h^–1. The density of air at its height is 1.2 kg m^–3. The fractional increase in the speed of the air on the upper surface of its wings relative to the lower surface is (Take g = 10 m s^–2)
a) 0.04
b) 0.08
c) 0.17
d) 0.34
Answer: c 

Question: An ideal fluid flows through a pipe of circular cross-section made of two sections with diameters 2.5 cm and 3.75 cm. The ratio of the velocities in the two pipes is
a) 9 : 4
b) 3 : 2
c) √3 : √2
d) √2 : √3
Answer: a

Question: Two liquids drops coalesce to form a large drop. Now,
a) energy is liberated
b) energy is neither liberated nor absorbed
c) some mass gets converted into energy
d) energy is absorbed
Answer: a 

Question: A cylindrical vessel is filled with water up to height H. A hole is bored in the wall at a depth h from the free surface of water. For maximum range, h is equal to
a) H/4
b) H/2
c) 3H/4
d) H
Answer: b

Question: The difference between viscosity and solid friction is/are
a) viscosity depends on area while solid friction does not
b) viscosity depends on nature of material but solid friction does not
c) both viscosity depends on area while solid friction does not and viscosity depends on nature of material but solid friction does not
d) neither viscosity depends on area while solid friction does not nor viscosity depends on nature of material but solid friction does not
Answer: a 

Question: A man is sitting in a boat which is floating in pond. If the man drinks some water from the pond, the level of water in the pond will
a) rise a little
b) fall a little
c) remain stationary
d) none of these
Answer: c

Question: The wettability of a surface by a liquid depends primarily on
a) density
b) angle of contact between the surface and the liquid
c) viscosity
d) surface tension.
Answer: b

Question: The constant velocity attained by a body while falling through a viscous medium is termed as
a) critical velocity
b) terminal velocity
c) threshold velocity
d) None of these
Answer: b

Question: The flow rate of water from a tap of diameter 1.25 cm is 3 L per min. The coefficient of viscosity of water is 10^–3 Pa s. The nature of the flow is Mechanical Properties of Fluids 25
a) Unsteady
b) Turbulent
c) Laminar
d) None of the options
Answer: b

Question: Paint-gun is based on
a) Bernoulli’s theorem
b) Archimedes’ principle
c) Boyle’s law
d) Pascal’s law
Answer: a

Question: Fevicol is added to paint to be painted on the walls, because
a) it increases adhesive force between paint and wall.
b) it decreases adhesive force between paint and wall molecules.
c) it decreases cohesive force between paint molecules.
d) None of the options
Answer: a

Question: A rectangular film of liquid is extended from (4 cm × 2 cm) to (5 cm × 4 cm). If the work done is 3 × 10^–4 J, the value of the surface tension of the liquid is
a) 0.250 N m^–1
b) 0.125 N m^–1
c) 0.2 N m^–1
d) 8.0 N m^–1
Answer: b

Question: Consider a 1 c.c. sample of air at absolute temperature T0 at sea level and another 1 c.c. sample of air at a height where the pressure is one-third atmosphere. The absolute temperature T of the sample at the height is
a) equal to T₀/3
b) equal to 3/T₀
c) equal to T₀
Answer: a

Question: The terminal velocity depends upon
a) 1/r
b) 1/r² 
c) 1/r³
d) r²
Answer: d

Question: A plane is in level fight at constant speed and each of its two wings has an area of 25 m². If the speed of the air on the upper and lower surfaces of the wing are 270 km h^–1 and 234 km h^–1 respectively, then the mass of the plane is (Take the density of the air = 1 kg m^–3)
a) 1550 kg
b) 1750 kg
c) 3500 kg
d) 3200 kg
Answer: c

Question: The velocity of efflux of a liquid through an orifice in the bottom of the tank does not depend upon
a) size of orifice
b) height of liquid
c) acceleration due to gravity
d) density of liquid
Answer: a

Question: At the boiling point of a liquid, surface tension
a) is zero
b) is infinite
c) is same as that at any other temperature
d) cannot be determined
Answer: a

Question: The surface energy of a liquid drop of radius r is proportional to
a) r³
b) r²
c) r
d) 1/r
Answer: b 

Question: Water is not used in thermometer because
a) it sticks to glass
b) its shows anamalous expansion
c) both it sticks to glass and its shows anamalous expansion
d) neither it sticks to glass nor its shows anamalous expansion
Answer: c

Question: In the figure, the velocity v₃ will be

a) zero
b) 4 m s^–1
c) 1 m s^–1
d) 3 m s^–1
Answer: c