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What will be the terminal velocity of a rain drop of radius (r) 1mm and mass (M) 0.001g falling through air. The coefficient of viscosity of air (η) is 1.8 X 10^-5Ns/m^2? Neglect buoyant force.(a) 20 m/s(b) 29.47 m/s(c) 35.8 m/s(d) 40 m/sI had been asked this question in a job interview.This interesting question is from Fluids Mechanical Properties topic in section Mechanical Properties of Fluids of Physics – Class 11

Answer»

The CORRECT OPTION is (B) 29.47 m/s

Explanation: At TERMINAL velocity, Mg = viscous force.Therefore, 0.001*10^-3*10 = 6πηrv∴ v = 10^-5/ 6πηr= 10^-5 / ( 6π*1.8 X 10^-5*0.001)= 29.47 m/s.



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