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Question

A tree breaks due to storm and the broken part bends, so that the top of the tree touches the ground making an angle of \(30^\circ\) with the ground. The distance between the foot of the tree to the point where the top touches the ground is 18 m. find the height of the tree (in metres).

This question was previously asked in
RRB ALP/Technician 2018 CBT 2 Electronics Mechanic Question Paper (23-Jan-2019) (Shift 1)
The correct answer is
$18\sqrt{3}$

Tree Breakage Geometry Setup

A tree breaks, and the broken part bends to touch the ground, forming a right-angled triangle with the remaining part of the tree and the ground.

  • The angle the top makes with the ground is \(\theta = 30^\circ\).
  • The distance from the foot of the tree to where the top touches the ground is the adjacent side, \(\text{adjacent} = 18\) m.
  • Let \(h\) be the height of the remaining part of the tree (opposite side).
  • Let \(x\) be the length of the broken part (hypotenuse).
  • The total height of the tree is \(h + x\).

Calculating Remaining Height (h)

We use the tangent function, which relates the opposite side and the adjacent side to the angle:

\(\tan(\theta) = \frac{\text{opposite}}{\text{adjacent}}\)

Substituting the known values:

\(\tan(30^\circ) = \frac{h}{18}\)

Solving for \(h\):

\(h = 18 \times \tan(30^\circ)\)

Since \(\tan(30^\circ) = \frac{1}{\sqrt{3}}\):

\(h = 18 \times \frac{1}{\sqrt{3}} = \frac{18}{\sqrt{3}}\)

Rationalizing the denominator:

\(h = \frac{18\sqrt{3}}{3} = 6\sqrt{3} \text{ m}\)

Calculating Broken Part (x)

We use the cosine function, which relates the adjacent side and the hypotenuse to the angle:

\(\cos(\theta) = \frac{\text{adjacent}}{\text{hypotenuse}}\)

Substituting the known values:

\(\cos(30^\circ) = \frac{18}{x}\)

Solving for \(x\):

\(x = \frac{18}{\cos(30^\circ)}\)

Since \(\cos(30^\circ) = \frac{\sqrt{3}}{2}\):

\(x = \frac{18}{\frac{\sqrt{3}}{2}} = \frac{18 \times 2}{\sqrt{3}} = \frac{36}{\sqrt{3}}\)

Rationalizing the denominator:

\(x = \frac{36\sqrt{3}}{3} = 12\sqrt{3} \text{ m}\)

Total Tree Height Calculation

The total height of the tree is the sum of the remaining height (\(h\)) and the length of the broken part (\(x\)):

\(\text{Total Height} = h + x\)

\(\text{Total Height} = 6\sqrt{3} \text{ m} + 12\sqrt{3} \text{ m}\)

\(\text{Total Height} = (6 + 12)\sqrt{3} \text{ m}\)

\(\text{Total Height} = 18\sqrt{3} \text{ m}\)

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Similar Questions

  1. A 1.8 m tall boy is standing at some distance from a 12 m tall building. The angle of elevation from his eyes to the top of the building increases from \(45^\circ\) to \(60^\circ\) as he walks towards the building. Find the distance (in meters) he walked towards the building.
  2. A 165cm tall man standing 500cm away from the wall looks at a hook on the wall with an angle of elevation of $45^\circ$. What is the height at which the hook is in the wall?
  3. The shadow of a candle fell on the table and made a right angled triangle with an angle of elevation of $60^\circ$ from the surface of the table to the upper tip of the flame of the candle. If the length of the candle is 21 cm, how long is the tip of the shadow on the table away from the base of the candle?
  4. In a right angled triangle, right-angled at $A$, the angle formed at $B$ is $45^\circ$, if the length of side $AB$ is 3m, then what is the length of the side $BC$?
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Important Questions from Heights and Distances

  1. Two pillars are placed vertically 8 feet apart. The height difference of the two pillars is 6 feet. The two ends of a rope of length 15 feet are tied to the tips of the two pillars. The portion of the length of the taller pillar that can be brought in contact with the rope without detaching the rope from the pillars is

  2. A 1.8 m tall boy is standing at some distance from a 12 m tall building. The angle of elevation from his eyes to the top of the building increases from \(45^\circ\) to \(60^\circ\) as he walks towards the building. Find the distance (in meters) he walked towards the building.
  3. A 165cm tall man standing 500cm away from the wall looks at a hook on the wall with an angle of elevation of $45^\circ$. What is the height at which the hook is in the wall?
  4. The shadow of a candle fell on the table and made a right angled triangle with an angle of elevation of $60^\circ$ from the surface of the table to the upper tip of the flame of the candle. If the length of the candle is 21 cm, how long is the tip of the shadow on the table away from the base of the candle?
  5. In a right angled triangle, right-angled at $A$, the angle formed at $B$ is $45^\circ$, if the length of side $AB$ is 3m, then what is the length of the side $BC$?
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