A telegraph post is bent at a point above the ground due to starm. Its top just touches the ground at a distance of 10 \sqrt3 metre from its foot and makes an angle of 30° with the horizontal. Then height (in metres) of the telegraph post is

SSC CGL Tier II 25 Oct 2015 Paper 1

Question : 21 of 100

Marks: +1, -0

A telegraph post is bent at a point above the ground due to starm. Its top just touches the ground at a distance of

10 √3

metre from its foot and makes an angle of 30° with the horizontal. Then height (in metres) of the telegraph post is

Solution:

(1)

AB = Telegraph post
AC = CD = bent part
BD =

10 √3

metreIn ΔBCD,

tan 30°= { {BC}}/{ {BD}}

⇒{1}/{√{3}}= { {BC}}/{10 \√{3}}

⇒{BC}= {1}/{√{3}} × 10 √{3}

= 10 metre
Again,

\sin 30°= { {BC}}/{ {CD}}

⇒{1}/{2}= {10}/{ {CD}}

⇒{CD}=20 {\metre}

∴{AB}=\ {BC}+ {CD}

=30 {\metre}

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