At `20.`C, to attain the terminal velocity how fast willan aluminium sphre of radii 1 mm fall though water. Assume flow to be laminar flow and specific gravity (AI) `=2.7eta_("water")=8xx10^(-4) Pa`

Options

A. `9.2 ms^(-1)`
B. `6.9 ms^(-1)`
C. `4.6 ms^(-1)`
D. `2.3 ms^(-1)`

Answer

C

Explanation

Specific gravity of Al=2.7
Density of air= `2.7xx10^(3)"kg m"^(-3)`
`"Terminal velocity"=(2r^(2)(p-sigma)g)/(9eta)`
`v=(2xx(1xx10^(-3))^(2)(2.7xx10^(3)-1000)xx9.8)/(8xx9xx10^(-4))`
Terminal velocity `v=4.6ms^(-1)`