(b) For sonometer $v \propto \frac{1}{l}$ $\therefore\ \frac{v_{1}}{v_{2}} = \frac{l_{2}}{l_{1}} \Longrightarrow \frac{256}{v_{2}} = \frac{16}{25}\ $ $v_{2} = \frac{256 \times 25}{16} = 400\ Hz$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.