Question

Three particles, each of mass ${10}^{-2}$ kg are brought from infinity to the vertices of an equilateral triangle of side $0.1m$, the work done is:

• A. $2\times {10}^{-8}J$
• B. $2\times {10}^{-11}J$
• C. $2\times {10}^{-12}J$
• D. $2\times {10}^{-13}J$

Answer 1

Answer: (D)

$2\times {10}^{-13}J$

Work done, $W=-U=-(-3\frac{G{m}^2}{r})=3\frac{G{m}^2}{r}$
$W=\frac{3\times 6.67\times {10}^{-11}\times ({10}^{-2}{)}^2}{{10}^{-1}}=2\times {10}^{-13}J$