Question

Wavelength of two notes is air $\frac{80}{195}$ m and $\frac{80}{193}$ m. Each note produces 5 beats per second with a third note of a fixed frequency. The speed of sound in air is:

• A. $300m{s}^{-1}$
• B. $340m{s}^{-1}$
• C. $375m{s}^{-1}$
• D. $400m{s}^{-1}$

Answer 1

The correct option is D $400m{s}^{-1}$

$f_1-f_0=5$
$f_a-f_2=5$
$\Rightarrow f_1-f_2=10$
$\frac{c}{\left(\frac{80}{195}\right)}-\frac{c}{\left(\frac{80}{193}\right)}=10$
$\Rightarrow \frac{2c}{80}=10$
$\Rightarrow C=400m{s}^{-1}$.