A ball is dropped from a height of 20 m 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 12.8 m above the water surface, the fish sees the speed of the ball as `[Take _(g)=10m/s^(2).]`

Options

A. `9 m//s`
B. `12 m//s`
C. `16 m//s`
D. `21.33 m//s`

Answer

C

Explanation

`x=(x)/(n_(rel)), v'=(v)/(n_(rel))=sqrt(2xx10xx(20-12.8))/(1)xx(4)/(3)=16 m//s.`