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Eight equal droplets of water each ofrad...

Eight equal droplets of water each ofradius rare falling through air with a terminal velocity of 7.5 `cm//s^2`. The drops coalesce to form a big drop in air. What will be the terminal velocity of the big drop.

A

15 cm/s

B

20 cm/s

C

25 cm/s

D

30 cm/s

Text Solution

Verified by Experts

The correct Answer is:
D
The radius of the big drop is calculated by using
`4/3piR^3=8(4/3pir^3)" ":." "R=2r`
But the terminal velocity`prop` (radius`)^2` according to Stoke's law
`(v_2)/(v_1=(K(2r)^2)/(K(r )^2)=4`
`:." "v_2=4xx7.5=30cm//s`
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