Explanation: \(\text{Solve: } \mu_1 = \rho \pi r_1^2 h; \, \mu_2 = \rho \pi r_2^2 h\) \(\frac{\mu_2}{\mu_1} = \frac{\pi \rho r_2^2 h}{\pi \rho r_1^2 h} = \frac{r_2^2}{r_1^2}\) \(\text{যেহেতু } r_2 = 3r_1, \, \frac{\mu_2}{\mu_1} = \frac{(3r_1)^2}{r_1^2} = \frac{9r_1^2}{r_1^2}\) \(\mu_2 = 9\mu_1 \implies \frac{\mu_1}{\mu_2} = \frac{1}{9}\) \(\text{আবার, } v = \sqrt{\frac{T}{\mu}}\) \(\frac{v_2}{v_1} = \sqrt{\frac{\mu_1}{\mu_2}} \, \text{[যেহেতু } T \text{ স্থির]}\) \(\frac{v_2}{v_1} = \sqrt{\frac{1}{9}} \implies v_2 = \frac{1}{3}v_1 \implies v_2 = \frac{1}{3} \times 1500 = 500 \, \text{ms}^{-1}\) \(\text{Ans. (B)}\)