Geometrical OpticsHard

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 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 ball as

Options

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

Solution

V2ball = 2 × 10 × 7.2
⇒   v = 12 m/s
Ximage of ball = Xball
Vimage of ball = Vball = × 12 = 16 m/s

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