Math Problem Statement

if the radius of a cone is twice its height and its volume is pi/6 cubic centimeter, what is its radius in cm?

Solution

The volume VV of a cone is given by the formula:

V=13πr2hV = \frac{1}{3} \pi r^2 h

where rr is the radius, and hh is the height.

Step 1: Relate rr and hh

We are given that the radius rr is twice the height hh, so:

r=2hr = 2h

Step 2: Substitute r=2hr = 2h into the volume formula

Substituting r=2hr = 2h into V=13πr2hV = \frac{1}{3} \pi r^2 h:

V=13π(2h)2hV = \frac{1}{3} \pi (2h)^2 h

Simplify (2h)2(2h)^2:

V=13π(4h2)h=13π(4h3)V = \frac{1}{3} \pi (4h^2) h = \frac{1}{3} \pi (4h^3)

V=43πh3V = \frac{4}{3} \pi h^3

Step 3: Solve for hh

We are given that V=π6V = \frac{\pi}{6}, so:

43πh3=π6\frac{4}{3} \pi h^3 = \frac{\pi}{6}

Cancel π\pi from both sides:

43h3=16\frac{4}{3} h^3 = \frac{1}{6}

Multiply through by 3:

4h3=124h^3 = \frac{1}{2}

Divide by 4:

h3=18h^3 = \frac{1}{8}

Take the cube root of both sides:

h=183=12h = \sqrt[3]{\frac{1}{8}} = \frac{1}{2}

Step 4: Find the radius rr

Since r=2hr = 2h, substitute h=12h = \frac{1}{2}:

r=2×12=1r = 2 \times \frac{1}{2} = 1

Final Answer:

The radius of the cone is:

1cm\boxed{1 \, \text{cm}}


Do you want more details or have any questions?
Here are 5 related questions to explore:

  1. How do you derive the volume formula for a cone?
  2. What is the relationship between radius and height in this cone?
  3. How would the solution change if the cone’s volume was doubled?
  4. How do you find the cube root of a fraction?
  5. Can you generalize this problem to cones where r=khr = k \cdot h?

Tip: Always simplify expressions before solving equations to avoid unnecessary complications.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Geometry
Volume of 3D Shapes
Algebraic Manipulation

Formulas

Volume of a cone: V = (1/3)πr²h

Theorems

-

Suitable Grade Level

Grades 8-10