Math Problem Statement

The tangents of a simple curve have bearings of N 20° E and N 80° E, respectively. The radius of the curve is 200 m. Compute the external distance of the curve

Solution

To solve this problem, we need to compute the external distance (also known as the external radius) of a simple circular curve. The external distance is the distance from the center of the curve to the tangent at the point of intersection between the tangents.

Step-by-step process:

  1. Understanding the Bearings: The bearings of the tangents are given as:

    • First tangent: N 20° E
    • Second tangent: N 80° E

    The angle between the tangents is the difference in the bearings. Since both bearings are measured from the North, we can compute the angle between them by subtracting the smaller bearing from the larger one:

    θ=8020=60\theta = 80^\circ - 20^\circ = 60^\circ

    So, the angle between the tangents is 60°.

  2. Given Information:

    • The radius (R) of the curve is 200 m.
    • The angle between the tangents (θ) is 60°.
  3. Formula for External Distance (E): The external distance EE can be computed using the following formula:

    E=Rcot(θ2)E = R \cdot \cot\left(\frac{\theta}{2}\right)

    Where:

    • RR is the radius of the curve (200 m).
    • θ\theta is the angle between the tangents (60°).
  4. Calculation:

    E=200cot(602)=200cot(30)E = 200 \cdot \cot\left(\frac{60^\circ}{2}\right) = 200 \cdot \cot(30^\circ)

    We know that cot(30)=1tan(30)=113=3\cot(30^\circ) = \frac{1}{\tan(30^\circ)} = \frac{1}{\frac{1}{\sqrt{3}}} = \sqrt{3}.

    So,

    E=20032001.732=346.4mE = 200 \cdot \sqrt{3} \approx 200 \cdot 1.732 = 346.4 \, \text{m}

Final Answer:

The external distance of the curve is approximately 346.4 meters.


Would you like a more detailed explanation of the formula or further clarifications?

Here are some related questions to expand your understanding:

  1. How do you calculate the internal distance of a circular curve?
  2. What is the relationship between the external distance and the length of the curve?
  3. How does the angle between tangents affect the external distance?
  4. What is the formula for computing the radius of a curve based on the external distance?
  5. How can the tangent bearings help in identifying the curve’s center point?

Tip: To always check if you've used the correct angle between tangents, verify the bearings are referenced from the same point, typically North or South, to avoid confusion when calculating the angle.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Geometry
Trigonometry
Circle Geometry

Formulas

E = R * cot(θ/2)

Theorems

Cotangent theorem
External distance formula for curves

Suitable Grade Level

Grades 11-12