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Question

If the cylinder and the cone shown have the same volume, then the radius and height of the cone could be which of these?

(2 points)
Responses

radius of the cone = 5; height of the cone = 4
radius of the cone = 5; height of the cone = 4

radius of the cone = 15; height of the cone = 12
radius of the cone = 15; height of the cone = 12

radius of the cone = 15; height of the cone = 4
radius of the cone = 15; height of the cone = 4

radius of the cone = 5; height of the cone = 12

1 answer

To determine which option provides the same volume for both the cone and the cylinder, we need to use the volume formulas for both shapes.

  1. Volume of the Cylinder (V_cylinder): \[ V_{cylinder} = \pi r_{cylinder}^2 h_{cylinder} \]

  2. Volume of the Cone (V_cone): \[ V_{cone} = \frac{1}{3} \pi r_{cone}^2 h_{cone} \]

Given that the volumes of the cone and the cylinder are equal, we set them equal to each other: \[ V_{cylinder} = V_{cone} \] \[ \pi r_{cylinder}^2 h_{cylinder} = \frac{1}{3} \pi r_{cone}^2 h_{cone} \]

Cancelling \(\pi\) from both sides and rearranging gives: \[ 3 r_{cylinder}^2 h_{cylinder} = r_{cone}^2 h_{cone} \]

We will compute this for each of the provided options (assuming we know the cylinder's radius and height):

Assuming some cylinder values, for instance, r_cylinder = 5 and h_cylinder = 12.

  • Option 1: radius of the cone = 5; height of the cone = 4 \[ 3(5^2)(12) = r_{cone}^2(4) \] \[ 3(25)(12) = 5^2(4) \implies 900 = 100 \quad \text{(FALSE)} \]

  • Option 2: radius of the cone = 15; height of the cone = 12 \[ 3(5^2)(12) = (15^2)(12) \] \[ 900 = 225 \cdot 12 \implies 900 = 2700 \quad \text{(FALSE)} \]

  • Option 3: radius of the cone = 15; height of the cone = 4 \[ 3(5^2)(12) = (15^2)(4) \] \[ 900 = 225 \cdot 4 \implies 900 = 900 \quad \text{(TRUE)} \]

  • Option 4: radius of the cone = 5; height of the cone = 12 \[ 3(5^2)(12) = (5^2)(12) \] \[ 900 = 300 \quad \text{(FALSE)} \]

Based on the calculations, the correct response indicating that the radius and height of the cone could be are:

radius of the cone = 15; height of the cone = 4.