CBSE Class 11 Physics Mechanical Properties Of Fluids Assignment

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 × 110^–6 m³/s
(c) 8.9 × 10^–6 m³/s
(d) 2.23 × 10^–6 m³/s
Answer. B

Question. A wind with speed 40 m/s blows parallel to the roof of a house. The area of the roof is 250 m². Assuming that the pressure inside the house is atmospheric pressure, the force exerted by the wind on the roof and the direction of the force will be (rair = 1.2 kg/m³)
(a) 2.4 × 10⁵ N, upwards
(b) 2.4 × 10⁵ N, downwards
(c) 4.8 × 10⁵5 N, downwards
(d) 4.8 × 10⁵ N, upwards
Answer. A

Question. A fluid is in streamline flow across a horizontal pipe of variable area of cross section. For this which of the following statements is correct?
(a) The velocity is maximum at the narrowest part of the pipe and pressure is maximum at the widest part of the pipe.
(b) Velocity and pressure both are maximum at the narrowest part of the pipe.
(c) Velocity and pressure both are maximum at the widest part of the pipe.
(d) The velocity is minimum at the narrowest part of the pipe and the pressure is minimum at the widest part of the pipe.
Answer. A

Question. Two small spherical metal balls, having equal masses, are made from materials of densities ρ₁ and ρ₂(ρ₁= 8ρ₂) and have radii of 1mm and 2 mm, respectively. They are made to fall vertically (from rest) in a viscous medium whose coefficient of viscosity equals h and whose density is 0.1 ρ₂. The ratio of their terminal velocities would be
(a) 79/72
(b) 19/36
(c) 39/72
(d) 79/36
Answer. D

Question. A small sphere of radius ‘r’ falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to
(a) r³
(b) r²
(c) r⁵
(d) r⁴ 
Answer. C

Question. A capillary tube of radius r is immersed in water and water rises in it to a height h. The mass of the water in the capillary is 5 g. Another capillary tube of radius 2r is immersed in water. The mass of water that will rise in this tube is
(a) 2.5 g
(b) 5.0 g
(c) 10.0 g
(d) 20.0 g 
Answer. C

Question. A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5 × 10^–2 N/m. The pressure inside the bubble equals at a point Z0 below the free surface of water in a container. Taking g = 10 m/s², density of water = 103 kg/m³, the value of Z0 is
(a) 0.5 cm
(b) 100 cm
(c) 10 cm
(d) 1 cm
Answer. D

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 Nm^–1
(d) 8.0 N m^–1
Answer. B

Question. Three liquids of densities ρ₁, ρ₂ and ρ₃ (with ρ₁ > ρ₂ > ρ₃), having the same value of surface tension T, rise to the same height in three identical capillaries. The angles of contact θ, θ₂ and θ₃ obey
(a) π/2 > θ₁ > θ₂ > θ₃ ≥ 0
(b) 0 ≤ θ < θ₂ < θ₃ < π/2
(c) π/2 < θ < θ₂ < θ₃ < p
(d) π > θ > θ₂ >  θ₃> π/2 
Answer. B

Question. Water rises to a height h in capillary tube. If the length of capillary tube above the surface of water is made less than h, then
(a) water rises upto a point a little below the top and stays there
(b) water does not rise at all
(c) water rises upto the tip of capillary tube and then starts overflowing like a fountain
(d) water rises upto the top of capillary tube and stays there without overflowing.
Answer. D

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