GATE AG 2008 • Q22 MCQ • 2 Marks

Section 1: Engineering Mathematics

Calculus

Subtopic: Limit, continuity and differentiability

Question Statement:

Cycloid is formed by x = a(θ−cosθ) and y = a(1−cosθ). The surface area of the curved plane obtained from the rotation of the cycloid around x axis is

Options:

  • (A) 16πa²/3
  • (B) 32πa²/3
  • (C) 64πa²/3
  • (D) 128πa²/3

Official Answer Key:

C

Step-by-Step Solution & Explanation

For the standard cycloid arch x=a(θ−sinθ), y=a(1−cosθ) rotated about the x-axis, the classical surface-of-revolution result (via S=∫2πy·ds over one arch, 0≤θ≤2π) is S = 64πa²/3. (The x-equation as printed uses cosθ rather than sinθ; taking this as a typographical rendering of the standard cycloid, the textbook result 64πa²/3 applies.) ⚠ Verification note: The parametrisation as printed (x=a(θ−cosθ)) departs from the standard cycloid (x=a(θ−sinθ)); treated as the standard cycloid form for evaluation, consistent with the official key.

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