Use the relationship among the formulas for the volumes of cones, cylinders, and spheres to solve the following problem. The volume of a cylinder is 36 cm3 . What is the volume of a sphere if its radius is the same as the cylinder’s and the height of the cylinder is equal to the sphere’s diameter?

1 answer

To find the volume of the sphere given the volume of the cylinder, we'll first outline the relationships and formulas for each of the shapes.

  1. Volume of a Cylinder: The volume \( V_c \) of a cylinder is given by the formula: \[ V_c = \pi r^2 h \] where \( r \) is the radius and \( h \) is the height.

  2. Volume of a Sphere: The volume \( V_s \) of a sphere is given by the formula: \[ V_s = \frac{4}{3} \pi r^3 \]

Given that the volume of the cylinder \( V_c \) is \( 36 , \text{cm}^3 \), we can write: \[ \pi r^2 h = 36 \]

Next, we are told that the height of the cylinder is equal to the diameter of the sphere. Since the diameter of the sphere is \( 2r \), we have: \[ h = 2r \]

Substituting \( h = 2r \) into the volume formula for the cylinder, we get: \[ \pi r^2 (2r) = 36 \] This simplifies to: \[ 2\pi r^3 = 36 \] Dividing both sides by \( 2\pi \): \[ r^3 = \frac{36}{2\pi} = \frac{18}{\pi} \]

Now, we can calculate \( r \): \[ r = \left(\frac{18}{\pi}\right)^{1/3} \]

Now we need to find the volume of the sphere using the radius \( r \). Plugging \( r^3 \) back into the sphere volume formula: \[ V_s = \frac{4}{3} \pi r^3 \] Substituting \( r^3 = \frac{18}{\pi} \): \[ V_s = \frac{4}{3} \pi \left(\frac{18}{\pi}\right) \] Simplifying this: \[ V_s = \frac{4}{3} \cdot 18 = \frac{72}{3} = 24 \]

Thus, the volume of the sphere is \( \boxed{24 , \text{cm}^3} \).