Question Detail
Question
Two small spheres carry charges of $0.0002 \text{ C}$ and $0.0004 \text{ C}$. If the electrostatic potential energy between them is $180 \text{ J}$, what is the distance separating their centers?
Correct Answer
Option B is the correct answer.
Detailed Explanation
Using $r = \frac{k \cdot q_1 \cdot q_2}{U}$, we have $r = \frac{(9 \times 10^9) \cdot (2 \times 10^{-4}) \cdot (4 \times 10^{-4})}{180}$. This simplifies to $r = \frac{720}{180} = 4.0 \text{ m}$.
Hint
Rearrange the formula $U = \frac{k \cdot q_1 \cdot q_2}{r}$ to solve for $r$ and remember $k = 9 \times 10^9$.