Volume of a Cone Math Example 4

Follow the full solution, then compare it with the other examples linked below.

Example 4

hard
A cone has a slant height of 13 cm and a radius of 5 cm. Find its volume. (Hint: use the Pythagorean theorem to find the height first.)

Solution

  1. 1
    Step 1: Use the Pythagorean theorem to find the vertical height. In a right triangle formed by the radius, height, and slant height: h2+r2=l2h^2 + r^2 = l^2, so h2+52=132h^2 + 5^2 = 13^2, giving h2=169โˆ’25=144h^2 = 169 - 25 = 144, thus h=12h = 12 cm.
  2. 2
    Step 2: Now compute the volume: V=13ฯ€r2h=13ฯ€(5)2(12)=13ฯ€ร—300=100ฯ€V = \frac{1}{3}\pi r^2 h = \frac{1}{3}\pi (5)^2 (12) = \frac{1}{3}\pi \times 300 = 100\pi cmยณ.

Answer

V=100ฯ€โ‰ˆ314.2V = 100\pi \approx 314.2 cmยณ.
The slant height, radius, and vertical height of a cone form a right triangle (the slant height is the hypotenuse). The vertical height is needed for the volume formula, so always convert slant height to vertical height using the Pythagorean theorem first. Notice 5-12-13 is a Pythagorean triple.

About Volume of a Cone

The amount of three-dimensional space inside a cone, which is exactly one-third the volume of a cylinder with the same base and height.

Learn more about Volume of a Cone โ†’

More Volume of a Cone Examples