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प्रश्न
A raindrop falls near the surface of the earth with almost uniform velocity because
पर्याय
its weight is negligible
the force of surface tension balances its weight
the force of viscosity of air balance its weight
the drops are charged and atmospheric electric field balances its weight.
उत्तर
Air has viscosity. During rainfall, the raindrops acquire acceleration due to gravity. However, the increase in velocity is hindered by the viscous force acting upwards. A gradual balance between the two opposing forces causes the raindrops to attain a terminal velocity, thus, falling with a uniform velocity.
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संबंधित प्रश्न
Fill in the blanks using the word(s) from the list appended with each statement
Viscosity of gases. .. with temperature, whereas viscosity of liquids . . . with temperature (increases / decreases)
Fill in the blanks using the word(s) 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)
Estimate the speed of vertically falling raindrops from the following data. Radius of the drops = 0.02 cm, viscosity of air = 1.8 × 10−4 poise, g= 9.9 × 10 ms−2 and density of water = 1000 kg m−3.
In a horizontal pipe of non-uniform cross-section, water flows with a velocity of 1 ms−1 at a point where the diameter of the pipe is 20 cm. The velocity of water (1.5 ms−1) at a point where the diameter of the pipe is (in cm)
Define terminal velocity.
Two streamlines cannot cross each other. Why?
Derive Poiseuille’s formula for the volume of a liquid flowing per second through a pipe under streamlined flow.
An incompressible liquid flows through a unifonn cross sectional tube with velocity 20 cm/s. If the thickness of liquid layer is 0.8 cm then velocity of gradient of flow is ____________.
Choose the CORRECT statement.
The tangential force or viscous drag on any layer of the liquid is directly proportional to the velocity gradient `"dv"/"dx"`. Then the direction of dx velocity gradient is ____________.
Clouds float in the air due to ______.
A solid ball of density ρ1 and radius r falls vertically through a liquid of density ρ2. Assume that the viscous force acting on the ball is F = krv, where k is a constant and v its velocity. What is the terminal velocity of the ball?
An air bubble of negligible weight having radius r rises steadily through a solution of density σ at speed v. The coefficient of viscosity of the solution is given by ______.
A spherical solid ball of volume V is made of a material of density ρ1. It is falling through a liquid of density ρ2 (ρ2 < ρ1). Assume that the liquid applies a viscous force on the ball that is proportional to the square of its speed v, i.e., `"F"_"viscous"`= -kv2 (k > 0). The terminal speed of the ball is ______.
State the formula and S.I. units of coefficient of viscosity.
Define velocity gradient.
State and explain Newton's law of viscosity.
A force of 0.01 N is required to move a flat glass plate of area of 10 cm2 with a uniform velocity of 1 cm/ s over the surface of a liquid 2 mm thick. If the coefficient of viscosity of the liquid is 20 poise, the velocity gradient in the liquid layer is ______.
The dimensions of coefficient of viscosity are ______.
A water pipe with diameter of 5.0 cm is connected to another pipe of diameter 2.5 cm. How would the speeds of the water flow compare?
