Coefficient of Viscosity

Q.

Viscosity of gases _______with temperature, whereas viscosity of liquids _______with temperature.

Q. A ball is thrown downward with some velocity into a viscous liquid. Draw graph that represents correct variation of velocity with time

Q.

Viscosity of gases _______with temperature, whereas viscosity of liquids _______with temperature.

1. decreases, decreases

2. increases, decreases

3. increases, increases

4. decreases, increases

Q.

The space between two large horizontal metal plates 6cm apart is filled with a liquid of viscosity $0.8Ns/m^2$ . A thin planck of surface area $1m^2$is moved parallel to the length of the plates such that the planck is at a distance of 2cm from one plate and 4cm from the other.The force F required to drag it with a constant speed of is $1m{s}^{-}1$ is

1. 80N

2. 20N

3. 60N

4. 40N

Q. The space between two plates $20\text{cm}\times 20\text{cm}\times 1\text{cm},1\text{cm}$ apart is filled with a liquid of viscosity $1\text{Poise}$. The upper plate is dragged to the right with a force of $F=5\text{N}$ keeping the lower plate stationary. The upper plate is moving at a constant speed $u$ as shown in figure.


What will be the velocity in $\text{m/s}$ of the flow at a point $0.5\text{cm}$ below the lower surface of the upper plate if linear velocity profile is assumed for the flow ?

1. $1.25$
2. $2.5$
3. $6.25$
4. $0.25$

Q.

The velocity of water in a river is 18 km h^-1 near the surface. If the river is 5 m deep, find the shearing stress between the horizontal layers of water. The coefficient of viscosity of water = 10^-2 poise.

1. 
2. 
3. 
4. 

Q.

Which of the following processes will be least affected by the viscosity of water ?

1. Water flowing through a pipe

2. Air bubble rising up through water

3. A wide, shallow sheet of water flowing on a flat surface

4. Water flowing out through a hole in the side of a tank

Q.

A long cylindrical rod of radius $R_1$ is placed co-axially inside a cylindrical tube of radius $R_2(>R_1)$ filled withviscous liquid and pulled along the axis with a constant velocity. In steady state the velocity gradient $\left(\frac{dv}{dr}\right)$ depends on the distance from the common axis 'r' as proportional to

1. $r^{\circ }$

2. $r^{-1}$

3. $r^{-2}$

4. $r^{-3}$

Q. Two drops of the same radius are falling through air with a steady velocity of 5 cm per sec. If the two drops coalesce, the terminal velocity would be

1. 10 cm per sec
2. 2.5 cm per sec
3. 
4. 

Q. Which of the following statements correctly gives the variation in the viscosities of a liquid and a gas with change in temperature?

1. Viscosity increases with increase in temperature for a liquid and decreases with increase in temperature for a gas
2. Viscosity increases with increase in temperature for a liquid and increases with increase in temperature for a gas
3. Viscosity decreases with increase in temperature for a liquid and decreases with increase in temperature for a gas
4. Viscosity decreases with increase in temperature for a liquid and increases with increase in temperature for a gas.

Q. A square plate of $1\text{m}$ side moves parallel to a second plate with velocity $4\text{m/s}$. A thin layer of water exist between plates. If the viscous force is $2\text{N}$ and the coefficient of viscosity is $0.01\text{Poise}$, then find the distance between the plates.

1. $4\text{mm}$
2. $3\text{mm}$
3. $2\text{mm}$
4. $1\text{mm}$

Q. Consider a gravity-free hall in which a tray of mass M, carrying a cubical block of ice of mass m and edge L, is at rest in the middle. If the ice melts, by what distance does the centre of mass of "the tray plus the ice" system descend?

Q.

Which of the following processes will be least affected by the viscosity of water ?

1. A wide, shallow sheet of water flowing on a flat surface

2. Water flowing out through a hole in the side of a tank

3. Water flowing through a pipe

4. Air bubble rising up through water

Q. We have three beakers containing glycerine, water and kerosene separately. They are stirred vigorously and placed on a 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

Q. The velocity of water in a river is $18\text{km/hr}$ at the surface. If the river is $5\text{m}$ deep, find the shearing stress between the horizontal layers of water. The viscosity of water is ${10}^{-2}\text{Poise}$.

1. ${10}^{-3}{\text{N/m}}^2$
2. $4\times {10}^{-3}{\text{N/m}}^2$
3. $3\times {10}^{-3}{\text{N/m}}^2$
4. $2\times {10}^{-3}{\text{N/m}}^2$

Q. A cubical block of side ${}^{\prime }{a}^{\prime }$ and density ${}^{\prime }{\rho }^{\prime }$ slides over a fixed inclined plane with constant velocity ${}^{\prime }{v}^{\prime }$ . There is a thin film of viscous fluid of thickness ${}^{\prime }{t}^{\prime }$ between the plane and the block. Then, the coefficient of viscosity of the thin film will be:
(Acceleration due to gravity is $g$)

1. $\frac{\rho ag\sin \theta t}{v}$
2. $\frac{\rho {agt}^2\text{sin}\theta }{v}$
3. $\frac{v}{\rho agt\sin \theta }$
4. None of these

Q. A Newtonian fluid fills the clearance between the shaft and the sleeve. When a force of $800\text{N}$ is applied to the shaft, parallel to the sleeve, the shaft attains a speed of $1.5\text{cm/sec}$. If a force of $2.4\text{kN}$ is applied instead, the shaft would move with a speed of

1. $1.5\text{cm/sec}$
2. $13.5\text{cm/sec}$
3. $4.5\text{cm/sec}$
4. None

Q. An air bubble of diameter $4\text{mm}$ rises steadily through a solution of density $1800{\text{kg/m}}^3$ at the rate of $0.05\text{m/s}$. Neglecting density of air, the co-efficient of viscosity of the solution is
[Take $g=10{\text{m/s}}^2$]

1. $0.64\text{poise}$
2. $6.4\text{poise}$
3. $0.32\text{poise}$
4. $3.2\text{poise}$

Q.

The space between two large horizontal metal plates 6cm apart is filled with a liquid of viscosity $0.8Ns/m^2$ . A thin planck of surface area $1m^2$is moved parallel to the length of the plates such that the planck is at a distance of 2cm from one plate and 4cm from the other.The force F required to drag it with a constant speed of is $1m{s}^{-}1$ is

1. 20N

2. 40N

3. 60N

4. 80N

Q. A liquid flowing through a horizontal pipeline of varying cross section. At a certain cross section, the diameter of the pipe is 5cm and the velocity of flow of liquid is 25cms-1. Calculate the velocity of flow at another cross section where the diameter of the pipe is 1cm.

Q. A large plastic plate of area $40{\text{m}}^2$ is floating on the surface of a river. Determine the tangential force that should be applied on the plastic plate to move the plate at $4\text{m/s}$ on the surface of the river. The depth of the river is $2\text{m}$ and coefficient of viscosity of water is ${10}^{-2}$ poise.

1. $0.16\text{N}$
2. $1.6\text{N}$
3. $0.08\text{N}$
4. $0.2\text{N}$

Q. The end of a capillary tube is immersed into a liquid. Liquid slowly rises in the tube up to some height. Then, the capillary - fluid system

1. Will absorb heat
2. Will release heat
3. Will not be involved in any heat transfer
4. Nothing can be said

Q. Consider the situation of the previous problem. Let the water push the left wall by a force F₁ and the right wall by a force F₂.
(a) F₁ = F₂
(b) F₁ > F₂
(c) F₁ < F₂
(d) the information is insufficient to know the relation between F₁ and F₂

Q.

The velocity of water in a river is 18 km h^-1 near the surface. If the river is 5 m deep, find the shearing stress between the horizontal layers of water. The coefficient of viscosity of water = 10^-2 poise.

1. 0.2 N

2. 0.02 N

3. 0.002 N

4. 2N

Q. A container filled with a viscous liquid is moving vertically downwards with a constant speed $3v_0$. At the instant shown, a sphere of radius $r$ is moving vertically downwards (in liquid) has speed $v_0$. There is no relative motion between fluid and container. The coefficient of viscosity is $\eta$. Then at the shown instant, the magnitude of viscous force acting on sphere is

1. $6\pi \eta r{v}_0$
2. $12\pi \eta r{v}_0$
3. $18\pi \eta r{v}_0$
4. $24\pi \eta r{v}_0$

Q. A cubical block of side ${}^{\prime }{a}^{\prime }$ and denisty ${}^{\prime }{\rho }^{\prime }$ slides over a fixed inclined plane with constant velocity ${}^{\prime }{v}^{\prime }$. There is a thin film of viscous fluid of thickness ${}^{\prime }{t}^{\prime }$ between the plane and the block. Then the coefficient of viscosity of thin film will be

1. $\frac{3\rho agt}{5v}$
2. $\frac{4\rho agt}{5v}$
3. $\frac{\rho agt}{v}$
4. None of these

Q.

Hot liquids flow faster than cold liquids? Explain

Q.

what happens when velocity of a liquidbecames greater than its critical velociy?

Q.

In a free fall motion from rest, Match column I to column II
column I
A) Graph between displacement and time
B) Graph between velocity and time
C) Graph between velocity and displacement
D) Graph between KE and displacement
column II
P) Parabola
Q) Straight line
C) Circle
D) No appropiate match given

Q. A boat of area $10{\text{m}}^2$ floating on the surface of a river is made to move horizontally with a speed of $2\text{m/s}$ by applying a tangential force. If the river is $1\text{m}$ deep and the water in contact with the bed is stationary, find the tangential force needed to keep the boat moving with same velocity. (Assume the viscosity of water as $0.01\text{poise}$).

1. $0.02\text{N}$
2. $0.03\text{N}$
3. $0.04\text{N}$
4. $0.05\text{N}$