Reasoning  A cylinder with radius 3 m and height 8 m has its radius quadrupled. How many times greater is the volume of the larger cylinder than the smaller​ cylinder? Use pencil and paper. Explain how the volume of the cylinder changes if its height were also quadrupled.

Question content area bottom
Part 1
The volume of the larger cylinder is
  
enter your response here times greater than the smaller cylinder.

1 answer

To solve this problem, we need to calculate the volumes of both the original (smaller) cylinder and the larger cylinder (with the radius quadrupled) and then determine how many times greater the larger cylinder's volume is than the smaller cylinder's volume.

Step 1: Calculate the Volume of the Original Cylinder

The volume \( V \) of a cylinder is given by the formula:

\[ V = \pi r^2 h \]

where:

  • \( r \) is the radius of the cylinder,
  • \( h \) is the height of the cylinder.

For the smaller cylinder:

  • Radius \( r = 3 \) m
  • Height \( h = 8 \) m

Substituting in the values:

\[ V_{\text{small}} = \pi (3^2)(8) = \pi (9)(8) = 72\pi \text{ cubic meters} \]

Step 2: Calculate the Volume of the Larger Cylinder

For the larger cylinder where the radius is quadrupled:

  • New radius \( r = 4 \times 3 = 12 \) m
  • Height remains the same at \( h = 8 \) m

Calculating the volume:

\[ V_{\text{large}} = \pi (12^2)(8) = \pi (144)(8) = 1152\pi \text{ cubic meters} \]

Step 3: Compare the Volumes

Now, we compare the volume of the larger cylinder to the smaller cylinder:

\[ \text{Volume ratio} = \frac{V_{\text{large}}}{V_{\text{small}}} = \frac{1152\pi}{72\pi} \]

The \( \pi \) cancels out:

\[ \text{Volume ratio} = \frac{1152}{72} = 16 \]

Conclusion for Part 1

The volume of the larger cylinder is 16 times greater than the smaller cylinder.

Step 4: How the Volume Changes if Height is Quadrupled

If the height of the larger cylinder is also quadrupled, the new height \( h' = 4 \times 8 = 32 \) m.

Now calculating the new volume with height quadrupled:

\[ V_{\text{new large}} = \pi (12^2)(32) = \pi (144)(32) = 4608\pi \text{ cubic meters} \]

Now, let's find the new volume ratio of the larger cylinder (with both radius and height quadrupled) to the small cylinder:

\[ \text{New volume ratio} = \frac{V_{\text{new large}}}{V_{\text{small}}} = \frac{4608\pi}{72\pi} \] Cancelling \( \pi \):

\[ \text{New volume ratio} = \frac{4608}{72} = 64 \]

Conclusion for Part 2

If both the radius and height of the cylinder are quadrupled, the volume of the larger cylinder becomes 64 times greater than the volume of the smaller cylinder.