NTSE Stage 2 SAT 2016 Question Paper

Question : 47 of 100

Marks: +1, -0

A person walks towards a tower. Initially when he starts, angle of elevation of the top of tower is 30°. On travelling 20 metres towards the tower, the angle changes to 60°. How much more has he to travel to reach the tower ?

$10√3$ metres
10 metres
20 metres
$10/√3$ metres

Validate

Solution:

In ∆DBC

\tan 60°=\x/\y

\x=√3\y

....(1)
Again in ∆DBC

\tan 30°=\x/{20+\y}

1/√3={√3\y}/{20+\y}

\y+20=3\y

2\y=20

\y=10 \m

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