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A bird is sitting on the top of a vertic...

A bird is sitting on the top of a vertical pole 20 m high and its elevation from a point O on the ground is `45o` . It flies off horizontally straight away from the point O. After one second, the elevation of the bird from O is reduced to `30o` . Then the speed (in m/s) of the bird is (1) `40(sqrt(2)-1)` (2) `40(sqrt(3)-2)` (3) `20""sqrt(2)` (4) `20(sqrt(3)-1)`

A

`40(sqrt(2)-1)`

B

`40(sqrt(3)-sqrt(2))`

C

`20sqrt(2)`

D

`20(sqrt(3)-1)`

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The correct Answer is:
D
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