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Question :
76. In order to overcome a surface tension of a : 2102182

76. In order to overcome a surface tension of a fluid, a force of 1.32 ´ 10^{-2} N is required to lift a wire ring of circumference 12.0 cm. What is the surface tension of the fluid?

A. 0.055 N/m

B. 0.11 N/m

C. 0.035 N/m

D. 0.018 N/m

77. A pipe of diameter three cm is replaced by one of the same length but of diameter six cm. If the pressure difference between the ends of the pipe remains the same, by what factor is the rate of flow of a viscous liquid through it changed?

A. 2

B. 4

C. 8

D. 16

78. Spherical particles of density 2.0 g/cm^{3} are shaken in a container of water (viscosity = 1.0 ´ 10^{-3} N?s/m^{3}). The water is 8.0 cm deep and is allowed to stand for 30 minutes. What is the greatest terminal velocity of the particles still in suspension at that time?

A. 0.55 ´ 10^{-5} m/s

B. 1.1 ´ 10^{-5} m/s

C. 2.2 ´ 10^{-5} m/s

D. 4.4 ´ 10^{-5} m/s

79. Spherical particles of density 2.0 g/cm^{3} are shaken in a container of water (viscosity = 1.0 ´ 10^{-3} N?s/m^{3}). The water is 8.0 cm deep and is allowed to stand for 30 minutes. What is the radius of the largest particles still in suspension at that time?

A. 4.5 ´ 10^{-6} m

B. 9.0 ´ 10^{-6} m

C. 2.3 ´ 10^{-6} m

D. 5.6 ´ 10^{-6} m

80. A centrifuge rotates at 100 rev/s (i.e., 628 rad/s). If the test tube places the suspension at 8.0 cm from the axis of rotation, by what factor are the terminal speeds of the settling particles increased as compared to sedimentation cause by gravity?

A. 3.2 ´ 10^{2}

B. 64

C. 800

D. 3.9 ´ 10^{5}