A particle rests in equilibrium under two forces of repulsion whose centres are at distances of $$a$$ and $$b$$ from the particle. The forces vary as the cube of the distance. The forces per unit mass are $$k$$ and $$k'$$ respectively. If the particle be slightly displaced towards one of them the motion is simple harmonic with the time period equal to

A

$$\frac{2\pi}{\sqrt{3\left(\frac{k}{a^3} + \frac{k'}{b^3}\right)}}$$

B

$$\frac{2\pi}{\sqrt{\left(\frac{k}{a^3} + \frac{k'}{b^3}\right)}}$$

C

$$\frac{2\pi}{\sqrt{\left(\frac{k}{a^4} + \frac{k'}{b^4}\right)}}$$

D

$$\frac{2\pi}{\sqrt{3\left(\frac{k}{a^4} + \frac{k'}{b^4}\right)}}$$