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Difficulty: MediumElementary Surveying Instruments and Fieldwork

During a prismatic compass survey of a farmland, a student records the forward bearing of line PQ as 125∘125^\circ. Assuming both stations are completely free from local attraction, what is the back bearing of line QP?

  1. 305∘305^\circAnswer
  2. B
    055∘055^\circ
  3. C
    215∘215^\circ
  4. D
    125∘125^\circ

Answer

The back bearing of line QP is 305∘305^\circ.
In prismatic compass surveying, the forward bearing and back bearing of any line differ by exactly 180∘180^\circ. When the forward bearing is less than 180∘180^\circ, adding 180∘180^\circ gives the back bearing (125∘+180∘=305∘125^\circ + 180^\circ = 305^\circ).

Step-by-Step Solution

1
Identify the forward bearing and check if it is greater or less than 180∘180^\circ.
The forward bearing is 125∘125^\circ, which is less than 180∘180^\circ.
The rule for converting forward bearing (FB) to back bearing (BB) depends on whether FB is greater than or less than 180∘180^\circ.
2
Apply the bearing conversion formula: BB=FB+180∘\text{BB} = \text{FB} + 180^\circ when FB<180∘\text{FB} < 180^\circ.
BB=125∘+180∘=305∘\text{BB} = 125^\circ + 180^\circ = 305^\circ.
Back bearing represents the opposite direction (180∘180^\circ difference) along the same line.

Key Concept

Forward and Back Bearing Conversion in Prismatic Compass Surveying
Estimated Time:1m 0s
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Topics

Elementary Surveying Instruments and Fieldwork

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