﻿ Why hydrogen filled balloon rises up and a C02 filled balloon falls down? from Physics Mechanical Properties of Fluids Class 11 Manipur Board

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Mechanical Properties of Fluids

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Why hydrogen filled balloon rises up and a C02 filled balloon falls down?

Hydrogen gas is lighter than air therefore, the weight of air displaced by hydrogen balloon is greater than the weight of hydrogen. Therefore, the buoyant force on the hydrogen balloon is greater than its weight and hence rises up. But CO2 is heavier than air thus, the buoyant force on CO2 balloon is less than its weight and hence it falls down.
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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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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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