# Coefficient of Viscosity

## Trending Questions

**Q.**

What is the significance of the Reynolds number?

**Q.**The velocity distribution for the flow over a flat plate is given by u=2y−y2 in which u is the velocity in m/s at a distance y metres above the plate. Determine the shear stress at y=0.15 m. Take dynamic viscosity of the fluid as 8.5 poise.

- 1.455 N/m2
- 1.445 N/m2
- 1.554 N/m2
- 1.545 N/m2

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

- Viscosity increases with increase in temperature for a liquid and decreases with increase in temperature for a gas
- Viscosity increases with increase in temperature for a liquid and increases with increase in temperature for a gas
- Viscosity decreases with increase in temperature for a liquid and decreases with increase in temperature for a gas
- Viscosity decreases with increase in temperature for a liquid and increases with increase in temperature for a gas.

**Q.**A cubical block of side ′a′ and density ′ρ′ slides over a fixed inclined plane with constant velocity ′v′ . There is a thin film of viscous fluid of thickness ′t′ between the plane and the block. Then, the coefficient of viscosity of the thin film will be:

(Acceleration due to gravity is g)

- ρagt2sin θv
- ρagsinθtv
- vρagtsinθ
- None of these

**Q.**There is a 1 mm thick layer of glycerine between a flat plate of area 100 cm2 & a big fixed plate. If the coefficient of viscosity of glycerine is 1.0 kg/m-s, then how much force is required to move the plate with a velocity of 7 cm/s?

- 7 N
- 0.7 N
- None of the above
- 0.007 N

**Q.**A boat of area 10 m2 floating on the surface of a river is made to move horizontally with a speed of 2 m/s by applying a tangential force. If the river is 1 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 poise).

- 0.02 N
- 0.03 N
- 0.04 N
- 0.05 N

**Q.**Water flows between two plates, of which the upper one is stationary and the lower one is moving with a velocity V. What will be the velocity of the fluid in contact with the upper plate?

- V
- V2
- 2V
- 0

**Q.**The velocity of water in a river is 18 kmh−1 near the surface. If the river is 5 m deep, then the shearing stress between the surface layer and the bottom layer is:

(Given - coefficient of viscosity of water, η=10−3 Pa.s)

- 10−4 Nm−2
- 10−5 Nm−2
- 10−2 Nm−2
- 10−3 Nm−2

**Q.**The shear stress at a point in a liquid is found to be 0.03 N/m2. The velocity gradient for the fluid flow is 0.15 s−1. What will be its viscosity (in Poise) ?

- 2
- 0.2
- 0.5
- 20

**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

- Glycerine
- Water
- Kerosene
- All of them at the same time

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

- 1.5 cm/sec
- 13.5 cm/sec
- 4.5 cm/sec
- None

**Q.**The space between two plates 20 cm×20 cm×1 cm, 1 cm apart is filled with a liquid of viscosity 1 Poise. The upper plate is dragged to the right with a force of F=5 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 m/s of the flow at a point 0.5 cm below the lower surface of the upper plate if linear velocity profile is assumed for the flow ?

- 1.25
- 2.5
- 0.25
- 6.25

**Q.**Two horizontal plates placed 250 mm apart have an oil layer of viscosity 20 poise in between the plates. Calculate the shear stress on the oil layer, if the upper plate is moved with a velocity of 1250 mm/s.

- 20 N/m2
- 2 N/m2
- 10 N/m2
- None of the above mentioned.

**Q.**A rectangular metal plate has dimensions of 10 cm×20 cm. A thin film of oil separates the plate from a fixed horizontal surface. The separation between the lower surface of the rectangular plate and the upper portion of the horizontal surface is 0.2 mm. An ideal string is attached to the plate and passes over an ideal pulley to a mass m. When m=125 gm, the metal plate moves at a constant speed of 5 cm/s across the horizontal surface. Then, the coefficient of viscosity of oil in dyne-s/cm2 is (Use g=1000 cm/s2)

- 5
- 25
- 2.5
- 50

**Q.**Which of the following graph shows the relation between shear stress and velocity gradient for a non-Newtonian fluid?

**Q.**

A sphere is dropped under gravity through a fluid of viscosity $h$. If the average acceleration is half of the initial acceleration, the time to attain the terminal velocity is $({\rho}_{s}=densityofthesphere,r=radius)$.

**Q.**A container filled with a viscous liquid is moving vertically downwards with a constant speed 3v0. At the instant shown, a sphere of radius r is moving vertically downwards (in liquid) has speed v0. There is no relative motion between fluid and container. The coefficient of viscosity is η. Then at the shown instant, the magnitude of viscous force acting on sphere is

- 6πηrv0
- 12πηrv0
- 18πηrv0
- 24πηrv0

**Q.**A plate of area 2 m2 is made to move horizontally with a speed of 2 m/s by applying a horizontal tangential force over the free surface of a liquid having depth of 1 m. If the coefficient of viscosity of liquid is 0.01 Poise, find the tangential force needed to move the plate.

- 4×10−3 N
- 3×10−3 N
- 2×10−3 N
- 1×10−3 N

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

- 3 mm
- 2 mm
- 1 mm
- 4 mm

**Q.**The ratio of radii of two wires of same material is 2:1. If these are stretched by equal forces, find the ratio of stress produced in them.

- 1 : 2
- 2 : 1
- 4 : 1
- 1 : 4

**Q.**A cubical block (side 2 m) of mass 20 kg slides on inclined plane lubricated with the oil of viscosity η=10−1 Poise with constant velocity of 10 m/s. Find out the thickness of the layer of liquid. (g=10m/s2)

- 4×10−3 m
- 3×10−3 m
- 2×10−3 m
- 1×10−3 m

**Q.**The velocity of water in a river is 18 km/hr at the surface. If the river is 5 m deep, find the shearing stress between the horizontal layers of water. The viscosity of water is 10−2 Poise.

- 10−3 N/m2
- 2×10−3 N/m2
- 3×10−3 N/m2
- 4×10−3 N/m2

**Q.**

Why do we treat air and vacuum similarly?Eg:The permittivity of air and vacuum is same

**Q.**The shear stress at a point in a liquid is found to be 0.03 N/m2. The velocity gradient for the fluid flow is 0.15 s−1. What will be its viscosity (in Poise) ?

- 20
- 2
- 0.2
- 0.5

**Q.**A man is rowing a boat with a constant velocity vo in a river of depth ′D′. The contact area of boat is ′A′ and coefficient of viscosity of water is η. Find the force required to row the boat.

- ηvoD
- ηA2voD
- ηD2voA
- ηAvoD

**Q.**The velocity distribution for the flow over a flat plate is given by u=2y−y2 in which u is the velocity in m/s at a distance y metres above the plate. Determine the shear stress at y=0.15 m. Take dynamic viscosity of the fluid as 8.5 poise.

- 1.455 N/m2
- 1.545 N/m2
- 1.445 N/m2
- 1.554 N/m2

**Q.**A square plate of 0.1 m side moves parallel to a second plate with a relative velocity of 0.1 m/s, both plates being immersed in water. If the viscous force is 0.002 N and the coefficient of viscosity is 0.01 Poise, distance between the plates in m is

- 0.1
- 0.05
- 0.005
- 0.0005

**Q.**There is a 1 mm thick layer of glycerine between a flat plate of area 100 cm2 & a big fixed plate. If the coefficient of viscosity of glycerine is 1.0 kg/m-s, then how much force is required to move the plate with a velocity of 7 cm/s?

- 7 N
- 0.7 N
- 0.007 N
- None of the above

**Q.**A ball is dropped in viscous liquid after some time it attains equilibrium, then

- v = 0
- v = horizontal
- v = constant
- v = variable

**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

- Will absorb heat
- Will release heat
- Will not be involved in any heat transfer
- Nothing can be said