Question: Express Y as the subject of the formula in the equation $2E = m(v^2 - y^2)$.
1. **State the problem:** We need to express $y$ as the subject of the formula from the equation $$2E = m(v^2 - y^2)$$.
2. **Write down the formula and rules:** The goal is to isolate $y$ on one side of the equation. We will use algebraic operations such as addition, subtraction, division, and taking square roots.
3. **Isolate the term containing $y^2$:**
$$2E = m(v^2 - y^2)$$
Subtract $m v^2$ from both sides:
$$2E - m v^2 = -m y^2$$
4. **Divide both sides by $-m$ to solve for $y^2$:**
$$\frac{2E - m v^2}{-m} = y^2$$
Show cancellation:
$$y^2 = \frac{\cancel{2E} - \cancel{m} v^2}{-\cancel{m}} = \frac{m v^2 - 2E}{m}$$
5. **Take the square root of both sides to solve for $y$:**
$$y = \pm \sqrt{\frac{m v^2 - 2E}{m}}$$
6. **Final answer:**
$$y = \pm \sqrt{v^2 - \frac{2E}{m}}$$
This means $y$ is equal to plus or minus the square root of $v^2$ minus $\frac{2E}{m}$.
This completes the solution.