Question : A pole of length 7 m is fixed vertically on the top of a tower. The angle of elevation of the top of the pole observed from a point on the ground is 60° and the angle of depression of the same point on the ground from the top of the tower is 45°. The height (in m) of the tower is:
Option 1: $7(2 \sqrt{3}-1)$
Option 2: $\frac{7}{2}(\sqrt{3}+2)$
Option 3: $7 \sqrt{3}$
Option 4: $\frac{7}{2}(\sqrt{3}+1)$
Correct Answer: $\frac{7}{2}(\sqrt{3}+1)$
Solution : Let pole be AD and tower be BD. Given, $AD = 7\ m$ In $\triangle BCD$ $\tan45^\circ = \frac{BD}{BC}$ ⇒ $1 = \frac{BD}{BC}$ ⇒ $BC = BD$ In $\triangle ABC$ $\tan60^\circ = \frac{AB}{BC}$ ⇒ $\sqrt3 = \frac{AB}{BC}$ ⇒ $AB = \sqrt3BC$ ⇒ $AD + BD = \sqrt3 BD$ ⇒ $\sqrt3BD - BD = 7$ ⇒ $BD(\sqrt3 - 1) = 7$ ⇒ $BD= \frac{7}{(\sqrt3 - 1)} × \frac{(\sqrt3 + 1)}{(\sqrt3 + 1)}$ $= \frac{7(\sqrt3 + 1)}{(\sqrt3)^2 - 1^2}$ $= \frac{7(\sqrt3 + 1)}{(3 - 1)}$ $= \frac{7}{2}(\sqrt3 + 1)$ Hence, the correct answer is $\frac{7}{2}(\sqrt3 + 1)$.
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Question : Two points A and B are on the ground and on opposite sides of a tower. A is closer to the foot of the tower by 42 m than B. If the angles of elevation of the top of the tower, as observed from A and B are 60° and 45°, respectively, then the height of the tower is closest to:
Option 1: 87.6 m
Option 2: 98.6 m
Option 3: 88.2 m
Option 4: 99.4 m
Question : If the angle of elevation of a balloon from two consecutive kilometre stones along a road are 30° and 60° respectively, then the height of the balloon above the ground will be:
Option 1: $\frac{\sqrt{3}}{2}$ km
Option 2: $\frac{1}{2}$ km
Option 3: $\frac{2}{\sqrt{3}}$ km
Option 4: $3\sqrt{3}$ km
Question : A 22 m long ladder (whose foot is on the ground) leans against a wall making an angle of 60° with the wall. What is the height (in m) of the point where the ladder touches the wall from the ground?
Option 1: $\frac{22 \sqrt{2}}{3}$
Option 2: $11 \sqrt{2}$
Option 3: $11$
Option 4: $11 \sqrt{3}$
Question : The angle of elevation of an aeroplane from a point on the ground is 60°. After 15 seconds of flight, the elevation changes to 30°. If the aeroplane is flying at a height of $1500\sqrt{3}$ metre, find the speed of the plane:
Option 1: 300 m/sec
Option 2: 200 m/sec
Option 3: 100 m/sec
Option 4: 150 m/sec
Question : From a point 12 m above the water level, the angle of elevation of the top of a hill is 60° and the angle of depression of the base of the hill is 30°. What is the height (in m) of the hill?
Option 1: $48 \sqrt{3}$
Option 2: $36$
Option 3: $36 \sqrt{3}$
Option 4: $48$
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