Question

A metal rod 40 cm long is dropped onto a wooden floor and rebounds into air. Compressional waves of many frequencies are thereby set up in the rod. If the speed of compressional waves in the rod is 5500 $m{s}^{-1}$ what is the - lowest frequency of compressional waves to which the rod resonates as it rebounds?

• A. 6875 Hz
• B. 16875 Hz
• C. 675 Hz
• D. 0.11 Hz

Answer 1

The correct option is A 6875 Hz

$L=2\left(\frac{\lambda }{4}\right)$

or$,$ $\lambda =2L=2\left(0.40m\right)=0.80m$

then$,$ from $\lambda =VT=\frac{V}{F}$

$F=\frac{V}{\lambda }=\frac{5500}{0.80}=6875Hz$

Hence,

option $\left(A\right)$ is correct answer.