A ball is dropped from a height of 20 m above the surface of water in a lake. The refractive index of water is 3 4 . A fish inside the lake, in the line of fall of the ball, is looking at the ball.

Question

A ball is dropped from a height of 20 m above the surface of water in a lake. The refractive index of water is 3 4 ​ . 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 ball as

TestHub · Accepted Answer

v = 2 g h ​ = 2 × 10 × 7 ​ = 12 ms − 1 In this case when eye is inside water, x app. ​ = μx ⇒ d t d x app. ​ ​ = μ ⋅ d t d x ​ or v app. ​ = μv = 3 4 ​ × 12 = 16 ms − 1

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JEE Main - 1 year (12th class)