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A fish rising up vertically toward the surface of water with speed `3ms^(-1)` observes a bird diving down vertically towards it with speed `9ms^(-1)` . The actual velocity of bird is

A

`4.5ms^(-1)`

B

`5.4ms^(-1)`

C

`3.0ms^(-1)`

D

`3.4ms^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
A
Effective height of the bird as seen by the fish,
`Y=y+muy^(')`
`(dY)/(dt)=(dy)/(dt)+mu(dy^('))/(dt)`
`9=3+(4)/(3)(dy^('))/(dt)`
or `(dy^('))/(dt)=(6xx3)/(4)=(18)/(4)=(9)/(2)=4.5ms^(-1)`
Therefore, actual velocity of bird `=4.5ms^(-1)`
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Knowledge Check

  • A bird is flying 3m above the surface of water,If the bird is diving vertically down with speed =6m//s his apparent velocity as seen by a stationary fish underwater is:

    A
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    B
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    C
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