Question : Two pillars A and B of the same height are on opposite sides of a road which is 40 m wide. The angles of elevation of the tops of the pillars A and B are $30^{\circ}$ and $45^{\circ}$, respectively, at a point on the road between the pillars. What is the distance (in m ) of the point from the foot of pillar A?
Option 1: $40(\sqrt{3}-1)$
Option 2: $20(2-\sqrt{3})$
Option 3: $20(3-\sqrt{3})$
Option 4: $39 \sqrt{3}$
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Correct Answer: $20(3-\sqrt{3})$
Solution : In $\triangle ROS$, $\tan45^\circ = \frac{h}{OS}$ ⇒ $1= \frac{h}{OS}$ $OS = h$ Thus, $QO = (40 - h)$ Now, In $\triangle POQ$, $\tan30^\circ = \frac{h}{40 - h}$ ⇒ $\frac{1}{\sqrt 3} = \frac{h}{(40 - h)}$ ⇒ $40 - h = \sqrt 3 h$ ⇒ $h (\sqrt 3 + 1) = 40$ ⇒ $h = \frac{40}{(\sqrt 3 + 1)}$ $QO = (40 - h)$ $QO=40 - \frac{40}{(\sqrt 3 + 1)}$ $QO = \frac{(40\sqrt 3)}{(\sqrt 3 + 1)}$ After rationalisation, we get: $QO = \frac{(40\sqrt 3)}{(\sqrt 3 + 1)}\times \frac{(\sqrt 3 - 1)}{(\sqrt 3 - 1)}$ $QO = 20(3 - \sqrt 3)$ Hence, the correct answer is $20(3 - \sqrt 3)$.
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Question : Two men standing on the same side of a pillar, 75 metres high, observe the angles of elevation of the top of the pillar to be $30^{\circ}$ and $60^{\circ}$, respectively. The distance between the two men is:
Option 1: $100\sqrt{3}$ m
Option 2: $100$ m
Option 3: $50\sqrt{3}$ m
Option 4: $25\sqrt{3}$ m
Question : The angle of elevation of the top of the pillar from the foot and the top of a building 20 m high, are 60° and 30°, respectively. The height of the pillar is:
Option 1: $10$ m
Option 2: $10\sqrt{3}$ m
Option 3: $60$ m
Option 4: $30$ 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 : A tower is broken at a point P above the ground. The top of the tower makes an angle of $60^\circ$ with the ground at Q. From another point R on the opposite side Q angle of elevation of point P is $30^\circ$. If QR = 180 m, what is the total height (in meters) of the tower?
Option 1: $90$
Option 2: $45\sqrt{3}$
Option 3: $45(\sqrt{3}+1)$
Option 4: $45(\sqrt{3}+2)$
Question : From a point on a bridge across the river, the angles of depression of the banks on opposite sides of the river are $30^{\circ}$ and $45^{\circ}$, respectively. If the bridge is at a height of 2.5 m from the banks, then the width of the river is: Take ($\sqrt{3}$ = 1.732).
Option 1: 5.83 metres
Option 2: 6.83 metres
Option 3: 5.76 metres
Option 4: 6.87 metres
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