When the sun's altitude changes from 30∘ to 60∘, the length of the shadow of a tower decreases by 70m. What is the height of the tower?
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Solution
Let AD be the tower, BD be the initial shadow and CD be the final shadow.
Given that BC=70m, ∠ABD=30∘ and ∠ACD=60∘
Let CD = x and AD = h.
From the right ΔCDA, tan60∘=ADCD √3=hx…(1)
From the right ΔBDA, tan30∘=ADBD 1√3=h70+x…(2)
Dividing (1) by (2) √31√3=hxh70+x ⇒3=70+xx ⇒2x=70 ⇒x=35
Substituting this value of x in (1), we have:- √3=h35 ⇒h=35√3=35×1.73=60.55≈60.6m