The terminal speed attained by an aluminium sphere of radius 1 mm falling through water at `20^@C` will be close to

Options

A. 9.2m/s
B. 6.9m/s
C. 4.6m/s
D. 2.3m/s

Answer

C

Explanation

`v_T=2/9 (r^2(rho-sigma)g)/(eta)`
`=2/9 xx ((10^(-3))^2 (2.7xx10^3 -10^3)xx9.8)/(8xx10^(-4))` = 4.6 m/s.