Mechanical Properties Of Fluids(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

MECHANICAL PROPERTIES OF FLUIDS MCQs

Total Questions : 29 | Page 2 of 3 pages

Question 11. When a capillary is dipped in water, water rises to a height h. If the length of the capillary is made less than h, then

The water will come out
The water will not come out
The water will not rise
The water will rise but less than height of capillary

Discuss Question

Answer: Option B. -> The water will not come out
:
B
Water rises to the top of the capillary tube and adjusts its meniscus shape and forms spherical surface but it can't come outside.

Question 12. A log of wood of mass 120 Kg floats in water. The weight that can be put on the raft to make it just sink should be (density of wood=600Kg/m³)

80 Kg
50 Kg
60 Kg
30 Kg

Discuss Question

Answer: Option A. -> 80 Kg
:
A
Volume of log of wood

V = \frac{m a s s}{d e n s i t y} = \frac{120}{600} = 0.2 m^{3}

Let x weight that can be put on the log of wood.
So weight of the body =

(120 + x) \times 10 N

Weight of displaced liquid =

V ρ g = 0.2 \times 10^{3} \times 10 N

The body will just sink in liquid if the weight of the body will be equal to the weight of displaced liquid.

(120 + x) \times 10 N = 0.2 \times 10^{3} \times 10 N

\Rightarrow x = 80 k g

Question 13. Which of the following processes will be least affected by the viscosity of water ?

Water flowing through a pipe
Air bubble rising up through water
A wide, shallow sheet of water flowing on a flat surface
Water flowing out through a hole in the side of a tank

Discuss Question

Answer: Option D. -> Water flowing out through a hole in the side of a tank
:
D
When water flows out of a hole in a tank, it is in contact with the edges of the hole over a very small area, and therefore viscosity effects are small

Question 14. A cylinder of height 20 m is completely filled with water. The velocity of efflux of water (in m/s) through a small hole on the side wall of the cylinder near its bottom is

10
20
25.5
5

Discuss Question

Answer: Option B. -> 20
:
B

v = \sqrt{2 g h} = \sqrt{2 \times 10 \times 20} = 20 m / s

Question 15. It is not possible to write directly on blotting paper or newspaper with ink pen

Because of viscosity
Because of inertia
Because of friction
Because of capillarity

Discuss Question

Answer: Option D. -> Because of capillarity
:
D
Due to capillarity it absorbs the ink.

Question 16. An incompressible liquid flows through a horizontal tube as shown in the following fig. Then the velocity v of the fluid is

3.0 m/s
1.5 m/s
1.0 m/s
2.25 m/s

Discuss Question

Answer: Option C. -> 1.0 m/s
:
C
If the liquid is incompressible then mass of liquid entering through left end, should be equal to mass of liquid coming out from the right end.

∴ M = m_{1} + m_{2} \Rightarrow A v_{1} = A v_{2} + 1.5 A . v

\Rightarrow A \times 3 = A \times 1.5 + 1.5 A . v \Rightarrow v = 1 m / s

Question 17. A metallic block of density 5 gm

c m^{- 3}

and having dimensions 5 cm

\times

5 cm

\times

5 cm is weighed in water. Its apparent weight will be

5×5×5×5 gf
4×4×4×4 gf
5×4×4×4 gf
4×5×5×5 gf

Discuss Question

Answer: Option D. -> 4×5×5×5 gf
:
D
Apparent weight

= V (ρ - σ) g = l \times b \times h \times (5 - 1) \times g

= (5 \times 5 \times 5 \times 4 \times g)

dyne =

(4 \times 5 \times 5 \times 5) g f

Question 18. A silver ingot weighing 2.1 kg is held by a string so as to be completely immersed in a liquid of relative density 0.8. The relative density of silver is 10.5. The tension in the string in kg-wt is

1.6
1.94
3.1
5.25

Discuss Question

Answer: Option B. -> 1.94
:
B
Apparent weight =

V (ρ - σ) g = \frac{M}{ρ} (ρ - σ) g

= M ⟮ 1 - \frac{σ}{ρ} ⟯ g = 2.1 ⟮ 1 - \frac{0.8}{10.5} ⟯ g = 1.94 g N

= 1.94 K g - w t

Question 19. In which one of the following cases will the liquid flow in a pipe be most streamlined

Liquid of high viscosity and high density flowing through a pipe of small radius
Liquid of high viscosity and low density flowing through a pipe of small radius
Liquid of low viscosity and low density flowing through a pipe of large radius
Liquid of low viscosity and high density flowing through a pipe of large radius

Discuss Question

Answer: Option B. -> Liquid of high viscosity and low density flowing through a pipe of small radius
:
B
For streamline flow, Reynold's number

N_{R} \propto \frac{r ρ}{η}

should be less. For less value of

N_{R}

, radius and density should be small and viscosity should be high.

Question 20. The excess of pressure inside a soap bubble than that of the outer pressure is

Discuss Question

Answer: Option B. -> 4Tr
:
B
The pressure inside the bubble is more than outside. Inside pressure -outside pressure =excess pressure. In the case of bubble excess pressure = 4S/R. where s is the surface tension and r is the radius.