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A ball is dropped from a height of 20m a...

A ball is dropped from a height of `20m` above the surface of water in a lake. The refractive index of water is `4//3`. A fish inside the lake, in the line of fall of the ball, is looking at the ball. At an instant, when the ball is `12.8m` above the water surface, the fish sees the speed of ball as `(g=10m//sec^2)`

A

9 m/s

B

12 m/s

C

16 m/s

D

21.33 m/s

Text Solution

Verified by Experts

The correct Answer is:
C
` v = sqrt(2 gh) = sqrt(2 xx 10 xx 7.2) = 12 m//s `
Height of the ball from surface as seen by fish
`h. = mu h rArr (dh.)/(dt) = mu (dh)/(dt)`
`rArr v. = mu v = (4)/(3) xx 12 = 16 m//s `
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