Viscosity is a property of:
1. liquids only
2. solids only
3. solids and liquids only
4. liquids and gases only

The force of viscosity is

1. electromagnetic

2. gravitational

3. nuclear

4. weak

The viscous force acting between two layers of a liquid is given by; \(\frac FA=-\eta\dfrac{dv}{dz}.\) 
This \((F/A)\) may be called:
1. pressure
2. longitudinal stress
3. tangential stress
4. volume stress

A raindrop falls near the surface of the earth with almost uniform velocity because

1. its weight is negligible

2. the force of surface tension balances its weight

3. the force of viscosity of air balances its weight

4. the drops are charged and atmospheric electric field balances its weight

A piece of wood is taken deep inside a long column of water and released. It will move up:

A solid sphere falls with a terminal velocity of 20 m s^–1 in air. If it is allowed to fall in vacuum,

1. terminal velocity will be 20 m s^–1

2. terminal velocity will be less than 20 m s^–1

3. terminal velocity will be more than 20 m s^–1

4. there will be no terminal velocity

A spherical ball is dropped in a long column of a viscous liquid. The speed of the ball (\(v\)) as a function of time (\(t\)) may be best represented by the graph:

                                   
1. \(\mathrm{D}\) 
2. \(\mathrm{B}\) 
3. \(\mathrm{A}\) 
4. \(\mathrm{C}\)

A solid sphere moves at a terminal velocity of 20 m s^–1 in air at a place where g = 9.8 m s^–2. The sphere is taken in a gravity-free hall having air at the same pressure and pushed down at a speed of 20 m s^–1.

(a) Its initial acceleration will be 9.8 m s^–2 downward

(b) Its initial acceleration will be 9.8 m s^–2  upward

(c) The magnitude of acceleration will decrease as the time passes

(d) It will eventually stop

Choose the correct option:

1. (a) and (b)

2. (b) and (c)

3. (a), (b) and (c)

4. (b), (c) and (d)