Nodal Voltages
1. **State the problem:** We need to find the nodal voltages $V_1$ and $V_2$ in the given circuit using nodal analysis.
2. **Identify nodes and reference:** Let the bottom node be the reference (ground) with voltage 0 V.
3. **Write nodal equations:**
- At node $V_1$:
The currents leaving $V_1$ through the 5 $\Omega$ resistor, 3 $\Omega$ resistor, and the connection to $V_2$ must sum to zero.
$$\frac{V_1 - 10}{5} + \frac{V_1 - V_2}{3} = 0$$
Here, $V_1 - 10$ is the voltage across the 5 $\Omega$ resistor (since the left side is connected to 10 V source).
- At node $V_2$:
The currents leaving $V_2$ through the 3 $\Omega$ resistor and the $\frac{4}{3}$ $\Omega$ resistor connected to 20 V source must sum to zero.
$$\frac{V_2 - V_1}{3} + \frac{V_2 - 20}{\frac{4}{3}} = 0$$
4. **Simplify equations:**
- Equation 1:
$$\frac{V_1 - 10}{5} + \frac{V_1 - V_2}{3} = 0$$
Multiply both sides by 15 (LCM of 5 and 3):
$$3(V_1 - 10) + 5(V_1 - V_2) = 0$$
$$3V_1 - 30 + 5V_1 - 5V_2 = 0$$
$$8V_1 - 5V_2 = 30$$
- Equation 2:
$$\frac{V_2 - V_1}{3} + \frac{V_2 - 20}{\frac{4}{3}} = 0$$
Note that dividing by $\frac{4}{3}$ is multiplying by $\frac{3}{4}$:
$$\frac{V_2 - V_1}{3} + \frac{3}{4}(V_2 - 20) = 0$$
Multiply both sides by 12 (LCM of 3 and 4):
$$4(V_2 - V_1) + 9(V_2 - 20) = 0$$
$$4V_2 - 4V_1 + 9V_2 - 180 = 0$$
$$13V_2 - 4V_1 = 180$$
5. **Solve the system of equations:**
From equation 1:
$$8V_1 - 5V_2 = 30$$
From equation 2:
$$-4V_1 + 13V_2 = 180$$
Multiply equation 1 by 4:
$$32V_1 - 20V_2 = 120$$
Multiply equation 2 by 8:
$$-32V_1 + 104V_2 = 1440$$
Add the two equations:
$$(32V_1 - 20V_2) + (-32V_1 + 104V_2) = 120 + 1440$$
$$84V_2 = 1560$$
$$V_2 = \frac{1560}{84} = \frac{130}{7} \approx 18.57\text{ V}$$
Substitute $V_2$ back into equation 1:
$$8V_1 - 5 \times \frac{130}{7} = 30$$
$$8V_1 = 30 + \frac{650}{7} = \frac{210}{7} + \frac{650}{7} = \frac{860}{7}$$
$$V_1 = \frac{860}{7 \times 8} = \frac{860}{56} = \frac{215}{14} \approx 15.36\text{ V}$$
6. **Final answer:**
$$V_1 = \frac{215}{14} \approx 15.36\text{ V}, \quad V_2 = \frac{130}{7} \approx 18.57\text{ V}$$