Question

A source emit sound waves of frequency 1000 $Hz$. The source moves to the right with a speed of 32 $m/s$ relative to ground. On the right a reflecting surface moves towards left with a speed 64 $m/s$ relative to ground. (speed of sound in air is 332 $m/s$)

• A. Wavelength of sound emitted by moving source is 0.3 m
• B. Number of wavefronts arriving per second which meets the reflected surface is 1320
• C. Speed of reflected wave is nearly 0.2 m
• D. Wavelength of reflected waves is nearly 0.2 m

Answer 1

Answer: (A), (B), (D)

The correct options are
A Wavelength of sound emitted by moving source is 0.3 m
B Number of wavefronts arriving per second which meets the reflected surface is 1320
D Wavelength of reflected waves is nearly 0.2 m

Wavelength of sound emitted by moving source is
${\lambda }_i=\frac{V-V_S}{f}=\frac{332-32}{1000}=0.3m$
Frequency of wave incident on reflector,
$f^{\prime }=f\frac{(V+V_0)}{V-V_S}=1000\times \frac{332+64}{332-32}=1320Hz$
Wavelength of reflected wave is,
${\lambda }_r=\frac{V-V_0}{f^{\prime }}=0.2m.$