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Sia

Question
Math
Posted 7 months ago

Julie is measuring two cones.
Given the base radius rr and height hh of the first cone, Julie uses the formula
V=πr2h3
V=\frac{\pi r^{2} h}{3}

to compute its volume VV to be 6 cubic meters.
The second cone has the same height, but has 2 times the radius. What is its volume?
Choose 1 answer:
(A) 12 cubic meters
(B) 4π4 \pi cubic meters
(C) 24 cubic meters
(D) 8π8 \pi cubic meters
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Answer from Sia
Posted 7 months ago
Solution by Steps
step 1
Given the formula for the volume of a cone V=πr2h3V = \frac{\pi r^2 h}{3} and V=6V = 6, solve for hh
step 2
Substitute V=6V = 6 into the formula to get 6=πr2h36 = \frac{\pi r^2 h}{3}
step 3
Multiply both sides by 33 to isolate πr2h\pi r^2 h on one side: 18=πr2h18 = \pi r^2 h
step 4
Divide both sides by πr2\pi r^2 to solve for hh: h=18πr2h = \frac{18}{\pi r^2}, with the condition that r0r \neq 0
step 5
For the second cone, the radius is twice that of the first cone, so the new radius is 2r2r
step 6
Use the volume formula for the second cone with the new radius: V=π(2r)2h3V = \frac{\pi (2r)^2 h}{3}
step 7
Substitute hh from step 4 into the new volume formula: V=π(2r)218πr23V = \frac{\pi (2r)^2 \cdot \frac{18}{\pi r^2}}{3}
step 8
Simplify the expression by canceling out π\pi and r2r^2: V=4183V = \frac{4 \cdot 18}{3}
step 9
Calculate the new volume: V=46=24V = 4 \cdot 6 = 24 cubic meters
[question 1] Answer
(C) 24 cubic meters
Key Concept
Scaling dimensions in geometric shapes
Explanation
When the radius is doubled, the area of the base is quadrupled because the area is proportional to the square of the radius. Since the height remains the same, the volume is also quadrupled.

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