d
રેખીય વેગમાન સંરક્ષણના નિયમ વડે \(m_1v_1 = m_2v_2\)

\( \Rightarrow \,\,\,\frac{{{m_1}}}{{{m_2}}}\,\,\, = \,\,\,\frac{{{v_2}}}{{{v_1}}}\,\,\, \Rightarrow \,\,\,\frac{{\frac{4}{3}\,\pi \,r_1^3\,d}}{{\frac{4}{3}\pi r_2^3\,d}}\,\,\, = \,\,\frac{{{v_2}}}{{{v_1}}}\,\,\,\,\,\, \Rightarrow \,\,\frac{{r_1^3}}{{r_2^3}}\,\,\, = \,\,\,\frac{1}{8}\,\,\,\,\,\,\, \Rightarrow \,\,\,\frac{{{r_1}}}{{{r_2}}}\,\, = \,\,\,\frac{1}{2}\)