Melted hemisphere forms a cylinder – Given CSA:TSA = 2:3, hemisphere radius 14 cm:\nA solid hemisphere of radius 14 cm is melted and cast into a cylinder. For the cylinder, curved surface area : total surface area = 2 : 3. Find the cylinder’s base radius (in cm).

Difficulty: Hard

Correct Answer: 9.71 cm

Explanation:


Introduction / Context:
Conservation of volume applies when reshaping solids. For a cylinder with CSA:TSA = 2:3, a fixed relation between height and radius follows. Combine with volume equality from the original hemisphere.


Given Data / Assumptions:

  • Hemisphere radius R = 14 cm.
  • For cylinder: CSA = 2πrh; TSA = 2πrh + 2πr^2; ratio 2:3.


Concept / Approach:
From CSA:TSA = 2:3 ⇒ h : (h + r) = 2 : 3 ⇒ h = 2r. Volume equality: hemisphere volume (2/3)πR^3 = cylinder volume πr^2h = πr^2(2r) = 2πr^3.


Step-by-Step Solution:

2πr^3 = (2/3)π * 14^3 ⇒ r^3 = (1/3)*14^3 = 2744/3.r = ∛(2744/3) ≈ 9.71 cm (rounded to two decimals).


Verification / Alternative check:
Then h = 2r ≈ 19.42 cm; check CSA:TSA = 2:3 by substitution holds algebraically.


Why Other Options Are Wrong:
10.33, 7.33, 12.33 cm deviate from the exact cube-root result. The originally printed choices were malformed; the repaired set includes the accurate value.


Final Answer:
9.71 cm

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