8RB Group D 23-Sep-2018 Shift 1 Solved Paper

Question : 85 of 100

Marks: +1, -0

The angle of elevation of a bird from a point 60

{m}

above the water in a pond is

30°.

The angle of depression of the reflection of the bird under the water from the same point is

60° .

Find the height of the bird in metres hovering over the pond.

Solution:

\Δ{AEB}, \tan 30°={{x}}/{{EB}}

{1}/{√{3}}={x}/{{ EB}}

⇒

E B=x \√{3}

....(1)
In

\Δ{EBD}, \tan 60°={{x}+60+60}/{{ EB}}

\√{3}={x+120}/{E B}

⇒

{EB}= { {x}+120}/{{ EB}}

...(2)
Solving (1)

\ \ &\ (2)

x=60

Thus, required height

=60+60=120 \ { m}

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