A string vibrates in five segments at a frequency of $460 mathrm{~Hz} .(a)$ What is its fundamental frequency? (b) What frequency will cause it to vibrate in three segments?
If the string is $n$ segments long, then fromwe have $nleft(frac{1}{2} lambda
ight)$ $=L$. But $lambda=v / f_{n}$, so $L=nleft(mathrm{u} / 2 f_{n}
ight)$. Solving for $f_{n}$ provides
$$
f_{n}=nleft(frac{v}{2 L}
ight)
$$
We are told that $f_{5}=460 mathrm{~Hz}$, and so
$$
460 mathrm{~Hz}=5left(frac{v}{2 L}
ight) quad ext { or } quad frac{v}{2 L}=92.0 mathrm{~Hz}
$$
Substituting this in the above relation gives
$$
f_{n}=(n)(92.0 mathrm{~Hz})
$$
(a) $f_{1}=92.0 mathrm{~Hz}$.
(b) $f_{3}=(3)(92 mathrm{~Hz})=276 mathrm{~Hz}$
Alternative Method
Recall that for a string held at both ends, $f_{n}=n_{f 1}$. Knowing that $f_{5}$ $=460 mathrm{~Hz}$, it follows that $f_{1}=92.0 mathrm{~Hz}$ and $f_{3}=276 mathrm{~Hz}$.