A small spherical ball of radius 0.1 mm and density 104 kg m–3 falls freely under gravity through a distance h before entering a tank of water. If, after entering the water the velocity of ball does not change and it continue to fall with same constant velocity inside water, then the value of h will be ______ m.
(Given g = 10 ms–2, viscosity of water = 1.0 × 10–5 N-sm–2).
(Given g = 10 ms–2, viscosity of water = 1.0 × 10–5 N-sm–2).
Correct Answer: 20
Solution and Explanation
The correct answer is 20
Speed after falling through height h, Should be equal to terminal velocity
\(\sqrt{2gh}\) = terminal speed
\(⇒ \sqrt{2gh} = \frac{2}{9} \frac{r²g(ρ-ρ′)}{η}\)
\(⇒ \frac{2}{9} × \frac{10^{-8} × 10 × 9000}{10^{-5}}\)
\(⇒ h = \frac{400}{2g}\)
⇒ h = 20 m
Therefore , the value of h will be 20 m
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Concepts Used:
Mechanical Properties of Fluid
The science of the mechanical properties of fluids is called Hydrostatics. A fluid is a substance that relents to the slightest pressure. Fluids are categorized into two classes famed by the names of liquids, and elastic fluids or gases, which later comprehend the air of the atmosphere and all the different kinds of air with which chemistry makes us acquainted.
Streamline Flow:
A streamline is a curve the tangent to which at any point provides the direction of the fluid velocity at that point. It is comparable to a line of force in an electric or magnetic field. In steady flow, the pattern of the streamline is motionless or static with time, and therefore, a streamline provides the actual path of a fluid particle.
Tube of Flow:
A tubular region of fluid enclosed by a boundary comprises streamlines is called a tube of flow. Fluid can never cross the boundaries of a tube of flow and therefore, a tube of flow acts as a pipe of the same shape.
Surface Tension and Viscosity:
The surface tension of a liquid is all the time a function of the solid or fluid with which the liquid is in contact. If a value for surface tension is provided in a table for oil, water, mercury, or whatever, and the contacting fluid is unspecified, it is safe to consider that the contacting fluid is air.