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).
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A8 cm
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B4 cm
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C7 cm
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D11 cm
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ENone of these
Answer
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