Optics Question 123

Question: A fish rising vertically up towards the surface of water with speed 3 ms?1 observes a bird diving vertically down towards it with speed 9 ms?1. The actual velocity of bird is

Options:

A) 4.5 ms?1

B) 5. ms?1

C) 3.0 ms?1

D) 3.4 ms?1

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Answer:

Correct Answer: A

Solution:

Here optical distance between fish and the bird is s=y+μy Differentiating w.r.t t we get dsdt=dydt+μdydt

Therefore 9=3+43dydt

Therefore dydt=4.5 m/sec



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