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प्रश्न
A raindrop falls near the surface of the earth with almost uniform velocity because
विकल्प
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)
(a) What is the largest average velocity of blood flow in an artery of radius 2 × 10–3 m if the flow must remain laminar? (b) What is the corresponding flow rate? (Take viscosity of blood to be 2.084 × 10–3 Pa s).
A metal sphere of radius 1 mm and mass 50 mg falls vertically in glycerine. Find (a) the viscous force exerted by the glycerine on the sphere when the speed of the sphere is 1 cm s−1, (b) the hydrostatic force exerted by the glycerine on the sphere and (c) the terminal velocity with which the sphere will move down without acceleration. Density of glycerine = 1260 kg m−3 and its coefficient of viscosity at room temperature = 8.0 poise.
With an increase in temperature, the viscosity of liquid and gas, respectively will __________.
Distinguish between streamlined flow and turbulent flow.
Write down the expression for Stoke’s force and explain the symbols involved in it.
Derive the expression for the terminal velocity of a sphere moving in a high viscous fluid using stokes force.
From amongst the following curves, which one shows the variation of the velocity v with time t for a small-sized spherical body falling vertically in a long column of a viscous liquid.
In motors, more viscous oil is used in summer than in winter due to ____________.
Analogy
Viscous force: ______:: Buoyant force: ______.
The velocity of a small ball of mass M and density d, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is `"d"/2`, then the viscous force acting on the ball will be ______
With increase in temperature, the viscosity of ______.
- gases decreases.
- liquids increases.
- gases increases.
- liquids decreases.
Is viscosity a vector?
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?
The velocity of a small ball of mass 0.3 g and density 8 g/cc when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is 1.3 g/cc, then the value of viscous force acting on the ball will be x × 10-4 N, and the value of x is ______.
[use g = 10 m/s2]
The coefficient of apparent expansion of mercury in a glass vessel is 153 × 10-6/°C and in a steel vessel is 144 × 10-6/°C. If α for steel is 12 × 10-6/°C, then that of glass is ______.
Define the coefficient of viscosity.
State the formula and S.I. units of coefficient of viscosity.
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?
