Question

A man is travelling towards east at 20ms${}^{-1}$ and sound waves are moving towards east at 340ms${}^{-1}$. He finds that $500$ waves cross him in $2$ seconds, the wavelength of the sound wave received by the man is :

• A. $1.28m$
• B. $2.28m$
• C. $3.28m$
• D. $4.28m$

Answer 1

The correct option is A $1.28m$

Speed of sound relate to man is $=340-20$ $=320m/s$
$f=\frac{numberofwavescrossing}{time}$$=\frac{500}{2}$$=250Hz$
$f=\frac{u}{\lambda }$
$\lambda =\frac{u}{f}$$=\frac{320}{250}$$=1.28m$