Question

A source of sound produces waves of wavelength $60cm$ when it is stationary. If the speed of sound in air is $320m{s}^{-1}$ and source moves with speed $20m{s}^{-1}$, the wavelength of sound in the forward direction will be nearest to :

• A. $56cm$
• B. $60cm$
• C. $64cm$
• D. $68cm$

Answer 1

The correct option is A $56cm$

Using formula,

$\Delta \lambda =\frac{u}{c}{\lambda }_0=\frac{20}{320}\times 60=3.75$

${\lambda }^{\prime }=60-3.75=56.25$ cm