A sphere of mass 40 kg is attraced by a second sphere of mass 15 kg when their centers are 20 cm apart, with a force of 0.1 milligram weight. Calculate the value of gravitational constant.

Weight, $W=0.1mgorforce,F=9.8\times {10}^{-6}N$

Using the expression, $G=F\times \frac{{r}^{2}}{{m}_{1}\times {m}_{2}}$

We get,

$G=\frac{9.8\times {10}^{-6}\times 0.2\times 0.2}{40\times 15}\phantom{\rule{0ex}{0ex}}=\frac{0.392\times {10}^{-6}}{600}=6.6\times {10}^{-11}N{m}^{2}/k{g}^{2}$

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