RRB NTPC Prelims Model Paper 4 with solutions

Question : 24 of 100

Marks: +1, -0

If the angle of elevation of the Sun changes from 30° to 45°, the length of the shadow of a pillar decreases by 20 metre. The height of the pillar is

Solution:

(4)

Let height of the pillar PQ be h mand length of shadow QR be a m.Therefore, QS will be (a – 20) m.
In △ PQS,

tan 45°{ PQ}/{QS}= h/{ a -20}⇒a =h+20

In △ PQR,

tan 30°={ PQ}/{QR}⇒ 1/√ 3

=h/a⇒h+ 20=√ 3h

Hence,

h=20/{√3-1}×{√3+1}/{√3+1}=10(√3+1)m

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