Question

Four identical point masses, each of mass $m$ and carrying charge $+q$ are placed at the corners of a square of sides '$a$' on a frictionless plain surface. If the particles are released simultaneously, the kinetic energy of the system when they are infinitely far apart is

• A. $ \frac{q^{2}}{a}(2 \sqrt{2}+1)$
• B. $\frac{q^{2}}{a}(\sqrt{2}+2)$
• C. $\frac{q^{2}}{a}(\sqrt{2}+4)$
• D. $\frac{q^{2}}{a}(\sqrt{2}+1)$

Answer 1

Answer: (C)

$K E_{i}+P E_{i}=K E_{f}+P E_{f}$
$\therefore K E_{i}+P E_{i}=4 \frac{K q^{2}}{a}+2 \frac{K q^{2}}{\sqrt{2} a}$
$=\frac{K q^{2}}{a}(4+\sqrt{2}), K =1$ in C.G.S. unit