Semicircle — If the area of a semicircle is 77 sq m, find its perimeter (use perimeter = πr + 2r for a semicircle).

Difficulty: Easy

Correct Answer: 36 m

Explanation:


Introduction / Context:
This problem tests formulas for a circle and a semicircle. For a semicircle of radius r, the area is (1/2) * π * r^2 and the perimeter (often called the boundary length) equals πr + 2r because it includes the curved arc (half the circumference) plus the diameter as the straight edge.



Given Data / Assumptions:

  • Area of semicircle = 77 sq m
  • Use π ≈ 22/7 for exact nice arithmetic
  • Perimeter of semicircle P = πr + 2r


Concept / Approach:
First recover the radius from the given area. Then plug r into the perimeter expression πr + 2r. With π = 22/7 here, the arithmetic becomes exact.



Step-by-Step Solution:
(1/2) * π * r^2 = 77(1/2) * (22/7) * r^2 = 77 ⇒ r^2 = 154 / (22/7) = 49 ⇒ r = 7 mPerimeter P = πr + 2r = (22/7)*7 + 14 = 22 + 14 = 36 m



Verification / Alternative check:
Back-substitute r = 7 in area formula for a semicircle to reconfirm 77 sq m, which matches the prompt exactly.



Why Other Options Are Wrong:
42 m, 48 m, and 54 m arise from misusing full circumference or omitting the diameter term; 32 m comes from mixing up half/whole factors.



Common Pitfalls:
Using full-circle perimeter 2πr or forgetting to add the diameter when computing the boundary length of a semicircle.



Final Answer:
36 m

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