Height & Distance – Wire length from angle Two poles are 20 m and 14 m high. Their tops are connected by a straight wire that makes a 30° angle with the horizontal. What is the length of the wire?

Difficulty: Easy

Correct Answer: 12 m

Explanation:


Introduction / Context:
When a straight wire spans between unequal heights, its inclination with the horizontal lets us relate the vertical difference to the wire’s length via basic trigonometry. The scenario forms a right triangle whose “opposite” is the height difference and whose hypotenuse is the wire.


Given Data / Assumptions:

  • Taller pole = 20 m; shorter pole = 14 m.
  • Wire joins their tops; inclination to horizontal = 30°.
  • Ground is level; wire is taut and straight.


Concept / Approach:
Let L be the wire length. Vertical rise between ends is Δh = 20 − 14 = 6 m. With angle θ to the horizontal, sin θ = (vertical rise)/L = Δh/L. Hence L = Δh / sin θ.


Step-by-Step Solution:

Δh = 6 msin 30° = 1/2L = Δh / sin 30° = 6 / (1/2) = 12 m


Verification / Alternative check:
Using components: vertical = L * sin 30° = L/2. Set L/2 = 6 ⇒ L = 12, consistent.


Why Other Options Are Wrong:
10 m and 8 m correspond to sin values inconsistent with 30° for a 6 m rise.


Common Pitfalls:
Accidentally using tan instead of sin (tan ties vertical to horizontal span, not to hypotenuse), or mixing which pole is taller.


Final Answer:
12 m

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