\(=\frac{\rho_{B} V g-\rho_{\pi} V g}{\rho_{B} V}\)
\(=\left(\frac{\rho_{B}-\rho_{\pi}}{\rho_{B}}\right) g \quad T=2 \pi \sqrt{\frac{\ell}{g}}\)
\(=\frac{5-1}{5} \times g\)
\(=\frac{4}{5} g\)
\(\frac{T^{\prime}}{T^{\prime}}=\sqrt{\frac{g}{g^{\prime}}}=\sqrt{\frac{g}{5} g}=\sqrt{\frac{5}{4}}\)
\(T^{\prime}=T \sqrt{\frac{5}{4}}=\frac{10}{2} \sqrt{5}\)
\(T^{\prime}=5 \sqrt{5}\)