-->

Circles

Question
CBSEENMA10008296

Two poles of equal heights are standing opposite each other on either side of the road, which is 80 m wide. From a point between them on the road, the angles of elevation of the top of the poles are 60° and 30°, respectively. Find the height of the poles and the distances of the point from the poles.

Solution

Let AD and BC be two poles of equal height h metres. Let P be a point on the road sucn that AP = x metres. Then BP = (80 - x) metres.
It is given that ∠APD = 60° and ∠BPC = 30°.
In right triangle APD, we have
tan space 60 degree space equals space AD over AP
rightwards double arrow space space space space square root of 3 space equals space straight h over straight x
rightwards double arrow space space space space space straight x space equals space fraction numerator straight h over denominator square root of 3 end fraction space space space space space space space space space space space space space space space... left parenthesis straight i right parenthesis
In right triangle BPC, we have
tan space 30 degree space space equals space BC over BP
rightwards double arrow space space space fraction numerator 1 over denominator square root of 3 end fraction equals fraction numerator straight h over denominator 80 minus straight x end fraction
rightwards double arrow space space space 80 minus straight x space equals space square root of 3 space straight h
rightwards double arrow space space space space straight x space equals space 80 space minus square root of 3 space straight h space space space space.... left parenthesis ii right parenthesis
Comparing (i) and (ii), we get
fraction numerator straight h over denominator square root of 3 end fraction space equals space 80 space minus square root of 3 space straight h
rightwards double arrow space space straight h space equals space square root of 3 space left parenthesis 80 minus square root of 3 straight h right parenthesis
rightwards double arrow space space straight h space equals space 80 square root of 3 space minus space 3 straight h
rightwards double arrow space space 4 space straight h space equals space 80 square root of 3
rightwards double arrow space space space straight h space equals space 20 square root of 3
Putting this value in eq. (i), we get
straight x space equals space fraction numerator straight h over denominator square root of 3 end fraction equals fraction numerator 20 square root of 3 over denominator square root of 3 end fraction equals 20 space straight m
And,    AP = x = 20 m
BP = 80 - x = 80 - 20 = 60 mHence, height of the poles equals 20 square root of 3 straight m.

Some More Questions From Circles Chapter