Answer
(a) $93.5Hz$
(b) $31.2Hz$
Work Step by Step
(a) We can find the required frequency as
$f_3=\frac{3v}{4L}$
We plug in the known values to obtain:
$f_3=\frac{3(343)}{4(4.75)}=93.5Hz$
(b) The fundamental frequency of the pipe can be determined as
$f_1=\frac{v}{4L}$
We plug in the known values to obtain:
$f_1=\frac{343}{2.75}=31.2Hz$
