Right circular cone — find base diameter from volume and height: The volume of a right circular cone is 48π cm3 and its height is 9 cm. Compute the diameter of the circular base (in centimeters).

Difficulty: Easy

Correct Answer: 8 cm

Explanation:


Introduction / Context:
This is a direct application of the cone volume formula with one unknown (the base radius). Once the radius is determined, the base diameter is twice the radius.



Given Data / Assumptions:

  • Height h = 9 cm.
  • Volume V = 48π cm3.
  • For a right circular cone, V = (1/3) * π * r^2 * h.
  • All dimensions are in centimeters; π is symbolic (exact cancellation occurs).


Concept / Approach:
Rearrange the cone volume formula to isolate r^2. Then compute the diameter D = 2r. The calculation is purely algebraic and does not need any approximation to π since π cancels out.



Step-by-Step Solution:
V = (1/3) * π * r^2 * h48π = (1/3) * π * r^2 * 948π = 3π * r^2 ⇒ r^2 = 48/3 = 16r = 4 cm ⇒ D = 2r = 8 cm



Verification / Alternative check:
Substitute r = 4, h = 9 back into V: (1/3)*π*16*9 = (1/3)*π*144 = 48π cm3, exactly as given.



Why Other Options Are Wrong:
4 cm is the radius, not diameter; 7 cm and 11 cm are arbitrary; they do not satisfy the cone volume with h = 9 cm.



Common Pitfalls:
Confusing radius with diameter; forgetting that r^2 appears in the formula; attempting to approximate π unnecessarily.



Final Answer:
8 cm

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