1.

Eight equal drops of water are falling through air with a stready 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 :

Answer»

40 cm `s^(-1)`
10 cm `s^(-1)`
`30cm s^(-1)`
`80cms^(-1)`

SOLUTION :Terminal velocity v`=(2r^(2))/(9eta)(p-sigma)G`
`rArrvpropr^(2)`
When 8 DROPS COMBINE to form a single drop then
`rArrR=2r`
`therefore(v_(2))/(v_(1))=(R^(2))/(r^(2))`
`(v_(2))/(v_(1))=(4R^(2))/(r^(2))=4`
`v_(2)=4v_(1)rArrv_(1)=4xx10=40` cm/s
So correct choice is (a).


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