Question

The relationships of the volumes of cylinders, cones, and spheres (considering that the height and radius are the same for all of the objects) are stated below.

Fill in the blank with the correct number.

(5 points)
A. One sphere +
cone(s) = one cylinder

B.
cone(s) = one cylinder

C.
cone(s) = one sphere

D. One sphere =
cylinder

E. One cone =
cylinder

1 answer

To fill in the blanks with the correct numerical relationships between the volumes of cylinders, cones, and spheres given the same height and radius, we can use the following volume formulas:

  1. Volume of a cylinder: \( V_{cylinder} = \pi r^2 h \)
  2. Volume of a cone: \( V_{cone} = \frac{1}{3} \pi r^2 h \)
  3. Volume of a sphere: \( V_{sphere} = \frac{4}{3} \pi r^3 \)

Let’s express these relationships mathematically for the identical dimensions (i.e., the height \( h \) and radius \( r \) are the same):

A. One sphere + cone(s) = one cylinder

  • From the formulas:
    \[ V_{sphere} + V_{cone} = V_{cylinder} \] \[ \frac{4}{3} \pi r^3 + \frac{1}{3} \pi r^2 h = \pi r^2 h \]
  • With \( h = r \): \[ \frac{4}{3} \pi r^3 + \frac{1}{3} \pi r^3 = \pi r^3 \]
  • Thus, one sphere + 2 cones = one cylinder.
    Fill in A: 2

B. (number of) cone(s) = one cylinder

  • As per the relationship:
    \[ V_{cone} = \frac{1}{3} V_{cylinder} \]
  • Therefore, 3 cones = one cylinder.
    Fill in B: 3

C. (number of) cone(s) = one sphere

  • Using the volume formulas and the fact that:
    \[ V_{sphere} = 2 \times V_{cone} \]
  • Thus, 2 cones = one sphere.
    Fill in C: 2

D. One sphere = (number of) cylinder

  • As we already established the relationship:
    • Since a sphere is equal to 1 cone and equal to 2 cones for being equal to 1 cylinder, one sphere is not equal to one cylinder. We can derive: \[ V_{sphere} = \frac{2}{3} V_{cylinder} \]
  • Thus, one sphere = (1.5) cylinder.
    Fill in D: \(1.5\)

E. One cone = (number of) cylinder

  • From \( 1 cone = \frac{1}{3} cylinder \):
  • Therefore, one cone = \( \frac{1}{3} \) cylinder.
    Fill in E: \( \frac{1}{3} \)

In summary, the completed blanks are:

A. 2
B. 3
C. 2
D. 1.5
E. 1/3