Neutron stars are believed to be composed of solid nuclear matter, primarily neutrons.
(a) If the radius of a neutron is $1.0 \times 10^{-13} \mathrm{cm},$ calculate its density in $\mathrm{g} / \mathrm{cm}^{3}$ (volume of a sphere $=\frac{4}{3} \pi r^{3}$ ).
(b) Assuming that a neutron star has the same density as a neutron, calculate the mass in kilograms of a small piece of a neutron star the size of a spherical pebble with a radius of $0.10 \mathrm{mm}$