Cone Volume A7680C
1. **Problem statement:**
A right triangle with hypotenuse $\sqrt{3}$ meters is revolved about one of its legs to form a right circular cone. We need to find the radius $r$, height $h$, and volume $V$ of the cone with the greatest volume.
2. **Setup and formula:**
Let the legs of the right triangle be $r$ and $h$. The hypotenuse is given by the Pythagorean theorem:
$$r^2 + h^2 = (\sqrt{3})^2 = 3$$
The volume of a cone is:
$$V = \frac{1}{3} \pi r^2 h$$
3. **Express volume in one variable:**
From the Pythagorean relation:
$$h = \sqrt{3 - r^2}$$
Substitute into volume formula:
$$V(r) = \frac{1}{3} \pi r^2 \sqrt{3 - r^2}$$
4. **Maximize volume:**
We find the critical points by differentiating $V(r)$ with respect to $r$ and setting it to zero.
Calculate derivative:
$$V'(r) = \frac{1}{3} \pi \left(2r \sqrt{3 - r^2} + r^2 \frac{d}{dr} \sqrt{3 - r^2} \right)$$
Compute derivative inside:
$$\frac{d}{dr} \sqrt{3 - r^2} = \frac{-r}{\sqrt{3 - r^2}}$$
So:
$$V'(r) = \frac{1}{3} \pi \left(2r \sqrt{3 - r^2} - \frac{r^3}{\sqrt{3 - r^2}} \right) = \frac{\pi r}{3 \sqrt{3 - r^2}} \left(2(3 - r^2) - r^2 \right) = \frac{\pi r}{3 \sqrt{3 - r^2}} (6 - 3r^2)$$
Set $V'(r) = 0$:
$$\frac{\pi r}{3 \sqrt{3 - r^2}} (6 - 3r^2) = 0$$
This gives:
- $r = 0$ (no volume)
- $6 - 3r^2 = 0 \Rightarrow r^2 = 2 \Rightarrow r = \sqrt{2}$ (valid since $r^2 \leq 3$)
5. **Find corresponding height:**
$$h = \sqrt{3 - r^2} = \sqrt{3 - 2} = 1$$
6. **Calculate maximum volume:**
$$V = \frac{1}{3} \pi r^2 h = \frac{1}{3} \pi (2)(1) = \frac{2\pi}{3}$$
**Final answers:**
- Radius $r = \sqrt{2}$ meters
- Height $h = 1$ meter
- Maximum volume $V = \frac{2\pi}{3}$ cubic meters