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Question

From the top of a platform 7 m high, the angle of elevation of a tower was 30°. If the platform was positioned 50√3 m away from the tower, how tall was the tower?

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is

57 m

Understanding the Problem: Finding Tower Height Using Angle of Elevation

This problem involves using trigonometry to find the height of a tower. We are given the height of a platform, the horizontal distance from the platform to the tower, and the angle of elevation from the top of the platform to the top of the tower.

Let's break down the given information:

  • Height of the platform = 7 m
  • Horizontal distance between the platform and the tower = \(50\sqrt{3}\) m
  • Angle of elevation from the top of the platform to the top of the tower = 30°

We need to find the total height of the tower.

Visualizing the Scenario and Setting up the Geometry

Imagine the platform and the tower standing vertically on the ground. The horizontal distance between them forms the base. From the top of the 7m high platform, a line of sight to the top of the tower creates the angle of elevation. If we draw a horizontal line from the top of the platform towards the tower, this line will be parallel to the ground and \(50\sqrt{3}\) m long. This horizontal line and the vertical segment representing the part of the tower above the platform's height form a right-angled triangle.

Let:

  • H be the total height of the tower.
  • h be the height of the platform (7 m).
  • x be the horizontal distance between the platform and the tower (\(50\sqrt{3}\) m).
  • y be the height of the tower above the top of the platform.

The total height of the tower is the sum of the platform's height and the additional height 'y', i.e., \(H = h + y\).

The angle of elevation (30°) is formed in the right-angled triangle between the horizontal line from the platform top and the line of sight to the tower top. In this triangle:

  • The side opposite the 30° angle is 'y' (the height above the platform top).
  • The side adjacent to the 30° angle is 'x' (the horizontal distance, \(50\sqrt{3}\) m).

Using Trigonometry to Find the Additional Height

We can use the tangent function, which relates the opposite side and the adjacent side in a right-angled triangle:

\(\tan(\text{angle of elevation}) = \frac{\text{Opposite side}}{\text{Adjacent side}}\)

In our case:

\(\tan(30^\circ) = \frac{y}{x}\)

Substitute the known values:

\(\tan(30^\circ) = \frac{y}{50\sqrt{3}}\)

We know that the value of \(\tan(30^\circ)\) is \(\frac{1}{\sqrt{3}}\).

So, the equation becomes:

\(\frac{1}{\sqrt{3}} = \frac{y}{50\sqrt{3}}\)

Now, we can solve for 'y':

\(y = \frac{1}{\sqrt{3}} \times 50\sqrt{3}\)

\(y = 50\) m

So, the height of the tower above the platform's top is 50 m.

Calculating the Total Height of the Tower

The total height of the tower is the height of the platform plus the height calculated above:

\(H = h + y\)

\(H = 7 \, \text{m} + 50 \, \text{m}\)

\(H = 57 \, \text{m}\)

Thus, the total height of the tower is 57 m.

Summary of Steps

  1. Identify the known values: platform height, horizontal distance, angle of elevation.
  2. Recognize that the problem forms a right-angled triangle above the platform height.
  3. Use the tangent function relating the angle of elevation, the unknown height above the platform (opposite side), and the horizontal distance (adjacent side).
  4. Substitute the values and solve for the unknown height.
  5. Add the platform height to the calculated height to find the total tower height.
Parameter Value
Platform Height (h) 7 m
Horizontal Distance (x) \(50\sqrt{3}\) m
Angle of Elevation 30°
Height above Platform (y) Calculated as 50 m
Total Tower Height (H) Calculated as 57 m

Revision Table: Key Trigonometry Concepts for Height and Distance Problems

Concept Description Trigonometric Ratio
Angle of Elevation The angle between the horizontal line of sight and the line of sight upwards to an object. Used in calculations involving looking upwards.
Angle of Depression The angle between the horizontal line of sight and the line of sight downwards to an object. Used in calculations involving looking downwards.
Tangent (\(\tan\)) Ratio of the length of the side opposite the angle to the length of the side adjacent to the angle in a right-angled triangle. \(\tan(\theta) = \frac{\text{Opposite}}{\text{Adjacent}}\)
Sine (\(\sin\)) Ratio of the length of the side opposite the angle to the length of the hypotenuse. \(\sin(\theta) = \frac{\text{Opposite}}{\text{Hypotenuse}}\)
Cosine (\(\cos\)) Ratio of the length of the side adjacent to the angle to the length of the hypotenuse. \(\cos(\theta) = \frac{\text{Adjacent}}{\text{Hypotenuse}}\)

Additional Information: Solving Height and Distance Problems

Problems involving heights and distances often require drawing a diagram to represent the situation correctly. Identifying the right-angled triangle is crucial. Based on what is given (angles, sides) and what needs to be found, you choose the appropriate trigonometric ratio (sin, cos, tan).

Remember common trigonometric values for standard angles like 0°, 30°, 45°, 60°, and 90°. In this problem, the value of \(\tan(30^\circ)\) was essential.

  • \(\sin(30^\circ) = 1/2\)
  • \(\cos(30^\circ) = \sqrt{3}/2\)
  • \(\tan(30^\circ) = 1/\sqrt{3}\)
  • \(\sin(45^\circ) = 1/\sqrt{2}\)
  • \(\cos(45^\circ) = 1/\sqrt{2}\)
  • \(\tan(45^\circ) = 1\)
  • \(\sin(60^\circ) = \sqrt{3}/2\)
  • \(\cos(60^\circ) = 1/2\)
  • \(\tan(60^\circ) = \sqrt{3}\)

Always ensure your calculations are accurate and pay attention to the units of measurement.

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Similar Questions

  1. The angle of depression of the foot of a building from the top of a tower 50 m away is 60°. How high is the tower?

  2. A ladder 13 m long reaches a window which is 12 m above the ground on side of a street. Keeping its foot at the same point, the ladder is turned to the other side of the street to reach a window 5 m high, then the width of the street is:

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  5. The angle of elevation of the top of a 36 m tall tower from the initial position of a person on the ground was 60°. She walked away in a manner that the foot of the tower, her initial position and the final position were all in the same straight line. The angle of elevation of the top of the tower from her final position was 30°. How much did she walk from her initial position?

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Important Questions from Heights and Distances

  1. Mohit is standing at some distance from a 60 meters tall building. Mohit is 1.8 meters tall. When Mohit walks towards the building, then the angle of elevation from his head becomes 60° from 45°. How much distance (in metres) Mohit covered towards the building?

  2. A peacock sitting at the top of a 3 meter high pole saw a snake approaching towards pole at a distance three times of the height of the pole. Then it jumping from pole will catch the snake at what distance from the pole if both are running with same speed ?

  3. The foot of a ladder 25 m long is 7 m from the base of the building. If the top of the ladder slips by 4 m, then by how much distance will the foot of the ladder slide?

  4. Two hotels stand 25 m apart. One of them is 70 m high and the angle of depression of the top of other as observed from the top of this hotel is 45°. Height of the other hotel is:

  5. A 7 m 20 cm pole casts a shadow of length 8 m 30 cm. Find the height of a tree that casts a shadow of length 6 m 64 cm, under similar conditions.

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