Question : The shadow of a tower when the angle of elevation of the sun is 45°, is found to be 10 metres longer than when it was 60°. The height of the tower is:
Option 1: $5\sqrt{3}-1$ metres
Option 2: $5(3+\sqrt{3})$ metres
Option 3: $10(\sqrt{3}-1)$ metres
Option 4: $10(\sqrt{3}+1)$ metres
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Correct Answer: $5(3+\sqrt{3})$ metres
Solution : Here, AB is the tower. BD is the shadow when $\angle$ADB = 45°, CB is the shadow when $\angle$ACB = 60°. By the given condition, CD = 10 m. In $\triangle$ADB, tan45° = $\frac{AB}{BD}$ ⇒$\frac{AB}{BC+CD} =1$ ⇒ AB = BC + 10 --(1) In △ACB, $\tan60° = \frac{AB}{BC}$ ⇒ $AB =\sqrt{3}BC$ --(2) From 1 and 2 we have, $BC + 10 = \sqrt{3}BC$ ⇒ $BC =\frac{10}{\sqrt{3}-1}=5(\sqrt{3}+1)$ m. $∴ AB = BC + 10 =5(\sqrt{3}+1)+10=5(\sqrt{3}+3)$ m Hence, the correct answer is $5(3+\sqrt{3})$ m.
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Question : The length of the shadow of a vertical tower on level ground increases by 10 m when the altitude of the sun changes from 45° to 30°. The height of the tower is:
Option 1: $10 \sqrt{3}$ m
Option 2: $5 \sqrt{3}$ m
Option 3: $5(\sqrt{3}+1)$ m
Option 4: $10(\sqrt{3}+1)$ m
Question : If the angle of elevation of the sun decreases from $45^\circ$ to $30^\circ$, then the length of the shadow of a pillar increases by 60 m. The height of the pillar is:
Option 1: $60(\sqrt{3}+1)$ metres
Option 2: $30(\sqrt{3}–1)$ metres
Option 3: $30(\sqrt{3}+1)$ metres
Option 4: $60(\sqrt{3}–1)$ metres
Question : From the top of a 20 metres high building, the angle of elevation from the top of a tower is 60° and the angle of depression of its foot is at 45°, then the height of the tower is: $(\sqrt{3} = 1.732)$
Option 1: 45.46 metres
Option 2: 45.64 metres
Option 3: 54.64 metres
Option 4: 54.46 metres
Question : If the length of the shadow of a vertical pole is $\sqrt{3}$ times the height of the pole, the angle of elevation of the sun is:
Option 1: $60°$
Option 2: $45°$
Option 3: $30°$
Option 4: $90°$
Question : The respective ratio between the height of the tower and the point at some distance from its foot is $5\sqrt{3}:5$. What will be the angle of elevation of the top of the tower?
Option 1: 30°
Option 2: 60°
Option 3: 90°
Option 4: 45°
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