Eight equal drops of water are falling through air with a steady velocity of 10 cm`s^(-1)`.If the drops combine to form a single drop big in size,then the terminal velocity of this big drop is

Options

A. 20 cm/s
B. 30 cm/s
C. 40 cm/s
D. 60 cm/s

Answer

C

Explanation

Here volume remains the same.
`therefore4/3piR^(3)=8 4/3pir^(3)`
`rArrR=2r`
Since terminal velocity, v`=2/(9eta).r^(2)[p-sigma]g`
`rArrvpropr^(2)`
`therefore` terminal velocity becomes 4 times as radius becomes double.
`therefore` New terminal velocity `= 4 xx 10` = 40 emfs.
Thus the correct choice is (c).