## Chapter Chosen

Mechanical Properties of Fluids

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The atmospheric pressure at sea level is 760mm of mercury. At what height it will be 740mm of mercury? Take the density of air 1.293kg/m3 constant upto height about 1 km.

Given, atmospheric pressure, P1= 760 mm of Hg
Atmospheric pressure, P2 = 740 mm of Hg
Density of air,

Let the height at which the atmospheric pressure is decreased be 'h'.

Now, Pressure due to h height of air = Pressure due to 2 cm or 0.02 m of mercury.

Threfore,

1.293 x g x h = 13600 x g x 0.02

$⇒$             h = 210 m, is the height at which the atmospheric pressure will decrease.
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Surface tension of liquids generally ....... with the temperature. (increases/decreases).

Decreases.
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Fill in the blanks using the words from the list appended with each statement:

For the model of a plane in a wind tunnel turbulence occurs at a .................. speed than the critical speed for turbulence for an actual plane. (greater/smaller)

Greater.
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Fill in the blanks using the words from the list appended with each statement:

For solids with elastic modulus of rigidity, the shearing force is proportional to ............ while for fluids it is proportional to ............... (shear strain/rate of shear strain).

Shear strain
, rate of shear strain.
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Explain why:
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than 100 km.

Near the sea level, density of air is the maximum. With increase in height from the surface, density of air decreases. At a height of about 6 km, density decreases to nearly half of its value at the sea level. Atmospheric pressure is proportional to density. Hence, at a height of 6 km from the surface, it decreases to nearly half of its value at the sea level.
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Fill in the blanks using the words from the list appended with each statement:

For a fluid in steady flow, the increase in flow speed at a constriction follows from .............while the decrease of pressure there follows from ................. (conservation of mass/Bernoulli's equation).

Conservation of mass,

Bernoulli's equation.

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