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-

9 m / s

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12 m / s

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16 m / s

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21.33 m / s

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Solution

The correct option is A $16 m / s$
$v_{b a 11}^{2} = 2 \times 10 \times 7.2$

$\Rightarrow v = 12 m / s$

$x_{i m a g e o f b a l l} = \frac{4}{3} X_{b a l l}$

$v_{i m a g e o f b a l l} = \frac{4}{3} V_{b a l l} = \frac{4}{3} \times 12 = 16 m / s$

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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-

The correct option is A 16 m/sv2ba11=2×10×7.2⇒v=12m/sximageofball=43Xballvimageofball=43Vball=43×12=16m/s

The correct option is A $16 m / s$
$v_{b a 11}^{2} = 2 \times 10 \times 7.2$

$\Rightarrow v = 12 m / s$

$x_{i m a g e o f b a l l} = \frac{4}{3} X_{b a l l}$

$v_{i m a g e o f b a l l} = \frac{4}{3} V_{b a l l} = \frac{4}{3} \times 12 = 16 m / s$