1. **State the problem:**
We want to find the volume $V$ of the solid obtained by rotating the region bounded by $y = x^2$, $y = mx$, and the $x$-axis around the $x$-axis using the Shell Method.
2. **Set up the problem:**
The Shell Method for rotation about the $x$-axis uses cylindrical shells formed by horizontal slices. The volume element is:
$$ dV = 2\pi \times (\text{radius}) \times (\text{height}) \times (\text{thickness}) $$
3. **Identify radius, height, and thickness:**
- Radius = distance from $x$-axis = $y$
- Height = horizontal length of the shell at height $y$
- Thickness = $dy$
4. **Express $x$ in terms of $y$ for the curves:**
From $y = x^2$, we get $x = \sqrt{y}$.
From $y = mx$, we get $x = \frac{y}{m}$.
5. **Determine the horizontal length (height of shell):**
At a fixed $y$, the shell extends from $x = \sqrt{y}$ to $x = \frac{y}{m}$.
So, height = $\frac{y}{m} - \sqrt{y}$.
6. **Find the limits for $y$:**
The curves intersect where $x^2 = mx \Rightarrow x^2 - mx = 0 \Rightarrow x(x - m) = 0$.
So $x=0$ or $x=m$.
At $x=0$, $y=0$.
At $x=m$, $y = m^2$.
Thus, $y$ goes from $0$ to $m^2$.
7. **Write the volume integral:**
$$ V = \int_0^{m^2} 2\pi y \left( \frac{y}{m} - \sqrt{y} \right) dy $$
8. **Simplify the integrand:**
$$ 2\pi y \left( \frac{y}{m} - \sqrt{y} \right) = 2\pi y \left( \frac{y}{m} \right) - 2\pi y \sqrt{y} = 2\pi \left( \frac{y^2}{m} - y^{3/2} \right) $$
9. **Integrate term-by-term:**
$$ V = 2\pi \int_0^{m^2} \left( \frac{y^2}{m} - y^{3/2} \right) dy = 2\pi \left[ \frac{1}{m} \int_0^{m^2} y^2 dy - \int_0^{m^2} y^{3/2} dy \right] $$
10. **Calculate each integral:**
$$ \int_0^{m^2} y^2 dy = \left[ \frac{y^3}{3} \right]_0^{m^2} = \frac{(m^2)^3}{3} = \frac{m^6}{3} $$
$$ \int_0^{m^2} y^{3/2} dy = \left[ \frac{y^{5/2}}{5/2} \right]_0^{m^2} = \frac{2}{5} (m^2)^{5/2} = \frac{2}{5} m^{5} $$
11. **Substitute back:**
$$ V = 2\pi \left( \frac{1}{m} \cdot \frac{m^6}{3} - \frac{2}{5} m^{5} \right) = 2\pi \left( \frac{m^5}{3} - \frac{2 m^5}{5} \right) $$
12. **Combine terms:**
Find common denominator 15:
$$ \frac{m^5}{3} = \frac{5 m^5}{15}, \quad \frac{2 m^5}{5} = \frac{6 m^5}{15} $$
So,
$$ V = 2\pi \left( \frac{5 m^5}{15} - \frac{6 m^5}{15} \right) = 2\pi \left( -\frac{m^5}{15} \right) = -\frac{2\pi m^5}{15} $$
Since volume cannot be negative, we take the absolute value:
$$ V = \frac{2\pi m^5}{15} $$
13. **Find volume when $m = \frac{1}{3}$:**
$$ V = \frac{2\pi}{15} \left( \frac{1}{3} \right)^5 = \frac{2\pi}{15} \cdot \frac{1}{243} = \frac{2\pi}{3645} $$
**Final answers:**
$$ V = \frac{2\pi m^5}{15} $$
$$ V \bigg|_{m=\frac{1}{3}} = \frac{2\pi}{3645} $$
Shell Method Volume 9B62B4
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