d
\(\mathrm{T}_{0}=2 \pi \sqrt{\frac{\mathrm{m}}{\mathrm{k}}}=\frac{2 \pi}{\sqrt{10}}\)

\(\mathrm{A}=\mathrm{A}_{0} \mathrm{e}^{-1 / \gamma}\)

\(\therefore\) for \(\mathrm{A}=\frac{\mathrm{A}_{0}}{\mathrm{e}}, \mathrm{t}=\gamma\)

\(\mathrm{t}=\gamma=\frac{2 \mathrm{m}}{\mathrm{b}}=\frac{\frac{2 \mathrm{m}}{\mathrm{B}^{2} \ell^{2}}}{\frac{\mathrm{B}^{2} \ell^{2}}{\mathrm{R}}}=10^{4} \,\mathrm{s}\)

\(\therefore \) No of oscillation \(\frac{\mathrm{t}}{\mathrm{T}_{0}}=\frac{10^{4}}{2 \pi / \sqrt{10}} \approx 5000\)