Answers

2015-09-17T15:14:14+05:30
We know the relation m =  \frac{density}{volume} . Now, volume of a sphere = \frac{4}{3}\pi r^{3} .

By the given data, radius = 0.21 cm. So volume = 0.039 cm3. Now, in SI units (m3), this is 3.9 x 10^-8 m3. 

So we have one variable, what about density? 7.8 g cm3 = 7.8 x 10^-9 kg m3.

Thus, mass (in kg) = 7.8 * 10^-9 / 3.9 * 10^-8 
                            = 200 gm. 
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