What will be the approximate terminal velocity of a rain drop of diameter $ 1.8\times {10}^{-3}. \mathrm{m}$, when density of rain water $ \approx {10}^{3}{\mathrm{kgm}}^{-3}$ and the coefficient of viscosity of air $ \approx 1.8\times {10}^{-5}. \mathrm{N}-\mathrm{sm}$$ {}^{-2} ?$ (Neglect buoyancy of air)
$ 98. {\mathrm{ms}}^{-1}$
Terminal velocity, $ v=\frac{2}{9}{r}^{2}\frac{(\rho -\sigma )}{\eta }g$
Neglecting buoyancy effect of the fluid,
$ v=\frac{2}{9}.\frac{\rho }{\eta }{r}^{2}g$
Putting the given values, we get
$ v=\frac{2}{9}\times \frac{{10}^{3}\times {\left(0.9\times {10}^{-3}\right)}^{2}}{1.8\times {10}^{-5}}\times 9.8=98\quad {\mathrm{ms}}^{-1}$
Important Questions from Physical and Thermal Properties of Bulk Matter
A wire of length 10 cm and diameter 0.5 mm is used in a bulb. The temperature of the wire is 1727°C and power radiated by the wire is 94.2 W. Its emissivity is $\frac{x}{8}$ where x =……
(Given $\sigma = 6.0 \times 10^{-8}$ W m$^{-2}$ K$^{-4}$, $\pi = 3.14$ and assume that the emissivity of wire material is same at all wavelength.)
A water drop of radius $1$ cm is broken into eight equal droplets. Surface tension of water is $0.075$ N $m^{-1}$. The gain in surface energy is __________$\times10^{-7}$ J.(Take $\pi = 3.14$)
- Two water drops of radius 'r' each coalesce to form a single large drop. If 'T' is the surface tension, then the surface energy released in this process is:
- Pressure of an ideal gas, contained in a closed vessel, is increased by $0.4\%$ when heated by $1^\circ C$. Its initial temperature must be:
A gas is kept in a container having walls which are thermally non-conducting. Initially the gas has a volume of $800 \ cm^3$ and temperature $27^{\circ}C$. The change in temperature when the gas is adiabatically compressed to $200 \ cm^3$ is:
(Take $\gamma = 1.5$; $\gamma$ is the ratio of specific heats at constant pressure and at constant volume)
