## Mechanical Properties of Fluids Questions and Answers Part-2

1. A small air bubble is at the inner surface of the bottom of a beaker filled with cold water. Now water of the beaker is heated. The size of bubble increases. The reason for this may be
a) Increase in the saturated vapour pressure of water
b) Root mean square velocity of air molecules inside the bubble increases
c) Decrease in surface tension of water
d) All of the above

Explanation: All of the above

2. The spiders and insects move and run about on the surface of water without sinking because
a) Elastic membrane is formed on water due to property of surface tension
b) Spiders and insects are lighter
c) Spiders and insects swim on water
d) Spider and insects experience upthrust

Explanation: Weight of spiders or insects can be balanced by vertical component of force due to surface tension

3. Small droplets of a liquid are usually more spherical in shape than larger drops of the same liquid because
a) Force of surface tension is equal and opposite to the force of gravity
b) Force of surface tension predominates the force of gravity
c) Force of gravity predominates the force of surface tension
d) Force of gravity and force of surface tension act in the same direction and are equal

Explanation: Force of surface tension predominates the force of gravity

4. Hairs of shaving brush cling together when it is removed from water due to
a) Force of attraction between hair
b) Surface tension
c) Viscosity of water
d) Characteristic property of hairs

Explanation: Surface tension

5.A square frame of side L is dipped in a liquid. On taking out, a membrane is formed. If the surface tension of the liquid is T, the force acting on the frame will be
a) 2 TL
b) 4 TL
c) 8 TL
d) 10 TL

Explanation: Force on each side = 2TL (due to two surfaces)
Force on the frame = 4(2TL) = 8TL

6.Water does not wet an oily glass because
a) Cohesive force of oil>> adhesive force between oil and glass
b) Cohesive force of oil > cohesive force of water
c) Oil repels water
d) Cohesive force for water > adhesive force between water and oil molecules

Explanation: Cohesive force for water > adhesive force between water and oil molecules

7. A water drop takes the shape of a sphere in a oil while the oil drop spreads in water, because
a) C.F. for water > A.F. for water and oil
b) C.F. for oil > A.F. for water and oil
c) C.F. for oil < A.F. for water and oil
d) None of the above

Explanation: C.F. for water > A.F. for water and oil

8. Which of the fact is not due to surface tension
a) Dancing of a camphor piece over the surface of water
b) Small mercury drop itself becomes spherical
c) A liquid surface comes at rest after stirring
d) Mercury does not wet the glass vessel

Explanation: This happens due to viscosity

9. In the glass capillary tube, the shape of the surface of the liquid depends upon
a) Only on the cohesive force of liquid molecules
b) Only on the adhesive force between the molecules of glass and liquid
c) Only on relative cohesive and adhesive force between the atoms
d) Neither on cohesive nor on adhesive force

d) 750 $\pi$ dynes
Explanation: The total length of the circular plate on which the force will act = 2 $\pi$ R
Force to pull = 2 $\pi$ RT = 2 * $\pi$ * 5 * 75 = 750 $\pi$ dynes