84. Calculate the velocity a spherical rain drop would achieve falling from 5.00 km (a) in the absence of air drag (b) with air drag. Take the size across of the drop to be 4 mm, the density to be 1.00 × 103 kg/m3 , and the surface area to be πr2 .

Respuesta :

Answer:

a) [tex]v=313.209\ m.s^{-1}[/tex]

b) [tex]v_t=3751.79\ m.s^{-1}[/tex]

Explanation:

Given:

  • height of the raindrop, [tex]h=5000\ m[/tex]

a)

[tex]v=\sqrt{2g.h}[/tex]

[tex]v=\sqrt{2\times 9.81\times 5000}[/tex]

[tex]v=313.209\ m.s^{-1}[/tex]

b)

given that:

diameter of the drop, [tex]d=4\ mm=0.004\ m[/tex]

density of the air, [tex]\rho=1.18\ kg.m^{-3}[/tex]

the terminal velocity is given as:

[tex]v_t=\sqrt{\frac{2m.g}{\rho.A.c_d} }[/tex]

where:

m = mass

g = acceleration due to gravity

[tex]\rho=[/tex] density of the medium through which the drop is falling (here air)

A = area normal to the velocity of fall

[tex]c_d=[/tex] coefficient of drag = 0.47 for spherical body

[tex]v_t=\sqrt{\frac{2\times 5\times 9.81}{1.18\times \pi\times 0.002^2\times 0.47} }[/tex]

[tex]v_t=3751.79\ m.s^{-1}[/tex]