Question

Three identical particles each of mass $m$ are placed at the corners of an equilateral triangle of side $l$. The work done by external force to increase the side of triangle from $l$ to $2l$ is

• A. $-\frac{3}{2}\frac{G{M}_2}{l}$
• B. $\frac{-3G{M}^2}{l}$
• C. $\frac{3}{2}\frac{G{M}_2}{l}$
• D. $\frac{3G{M}^2}{l}$

Answer 1

The correct option is C $\frac{3}{2}\frac{G{M}_2}{l}$

Work done $W=\Delta U=U_f-V_i$
$=3(-\frac{GMM}{2l})-3(-\frac{GMM}{l})$
$=\frac{3}{2}\frac{G{M}^2}{l}$