$\frac{{{v_{{T_2}}}}}{{0.2}} = \frac{{\left( {10.5 - 1.5} \right)}}{{\left( {19.5 - 1.5} \right)}} \Rightarrow {v_{{T_2}}} = 0.2 \times \frac{9}{{18}} = 0.1\,m/s$


$(A)$ the net elongation of the spring is $\frac{4 \pi R^3 \rho g}{3 k}$
$(B)$ the net elongation of the spring is $\frac{8 \pi R^3 \rho g}{3 k}$
$(C)$ the light sphere is partially submerged.
$(D)$ the light sphere is completely submerged.
