Tag: viscosity

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Questions Related to viscosity

Multiple choice viscosity option b: engineering physics properties of matter physics

Viscous force a is similar to friction in solids ,but viscous force
a. is independent of area but friction depends on area
b. is temperature dependent while friction force between solids depends upon normal reaction
c. is velocity dependent while friction is velocity independent

  1. a, b, c are correct

  2. a, c are correct

  3. b, c are correct

  4. a, b are correct
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Viscosity depends of mass of body, temperature, velocity and density.
Where as friction depends only on normal reaction.

Multiple choice viscosity option b: engineering physics properties of matter physics

The viscous force on a small sphere of radius $R$ moving in a fluid varies as 

  1. $\propto \ R^2$

  2. $\propto \ R$

  3. $\propto \ (\dfrac{1}{R})$

  4. $\propto \ (\dfrac{1}{R})^2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Stokes' Law, the viscous drag force F on a sphere of radius R moving at velocity v in a fluid is given by F = 6 * pi * eta * R * v. Thus, the force is directly proportional to the radius R.

Multiple choice viscosity option b: engineering physics properties of matter physics

Why does the cotton wick in an oil filled lamp keep on burning?

  1. By friction

  2. By capillary action

  3. By electrostatic force

  4. By Gravitational force
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Due to surface tension of oil capillary rise can be seen in cotton wick which makes lamp to burn.

Multiple choice viscosity option b: engineering physics properties of matter physics

When a ball is released from rest in a very long column of viscous liquid, its down ward acceleration is $a'$ (just after released). Its acceleration when it has acquired to third of the maximum velocity is $a/X$. Find the value of $X$.

  1. $2$

  2. $3$

  3. $23$

  4. $5$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The equation of motion for a falling sphere is m*a = mg - F_buoyant - F_viscous. At terminal velocity v_t, the net force is zero, so F_viscous = mg - F_buoyant. When v = v_t/3, the viscous force is F_viscous' = (1/3) * F_viscous. Substituting this, the acceleration becomes a' = (1 - 1/3) * g_effective = (2/3) * a_initial. The question asks for a/X, where a' = a/3, implying X=3.

Multiple choice viscosity option b: engineering physics properties of matter physics

A liquid rises in a capillary tube when the angle of contact is:

  1. $An\ acute\ one$

  2. $An\ obtuse\ one$

  3. $\pi/2\ radian$

  4. $\pi\ radian$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If angle of contact is acute, liquid rises in a capillary tube whereas if angle of contact is obtuse, liquid is depressed in a capillary tube.

Hence, option A is correct.

Multiple choice viscosity option b: engineering physics properties of matter physics

Two solid metal balls of radii $r$ $2r$ are falling with their terminal speeds in a viscous liquid.What is the ratio of drag force acting on these two balls?

  1. 1;2

  2. 1;4

  3. 1;8

  4. 4;1
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Terminal velocity v_t is proportional to r^2. The drag force F = 6 * pi * eta * r * v_t. Substituting v_t proportional to r^2, we get F proportional to r * r^2 = r^3. The ratio of forces for radii r and 2r is (r/2r)^3 = 1/8.

Multiple choice viscosity option b: engineering physics properties of matter physics

We have three beakers A, B and C containing glycerine, water and kerosene respectively. They are stirred vigorously and placed on the table. The liquid which comes to rest at the earliest is

  1. Glycerine

  2. Water

  3. Kerosene

  4. All of them at the same time
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The rate at which a stirred liquid comes to rest depends on its viscosity. Glycerine has the highest viscosity among the given liquids, causing it to dissipate kinetic energy through internal friction most rapidly.

Multiple choice viscosity option b: engineering physics properties of matter physics

When $200 ml$ of water is subjected to a pressure of $2 \times {10^8}pa,$ the decrease in its volume is $0.2 ml.$ the compressibility of water is -----

  1. $5 \times {10^{ - 8}}{m^2}{N^{ - 1}}$

  2. $5 \times {10^{ - 10}}{m^2}{N^{ - 1}}$

  3. $5 \times {10^{ - 12}}{m^2}{N^{ - 1}}$

  4. $None$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Compressibility K = -(1/V) * (dV/dP). Here, dV/V = 0.2 / 200 = 0.001. dP = 2 * 10^8 Pa. K = 0.001 / (2 * 10^8) = 0.5 * 10^-11 = 5 * 10^-12 m^2/N.