Question

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

• A. wavelength of reflected waves is nearly 0.3m
• B. number of waves arriving per second which meets the reflected surface is 1320
• C. speed of reflected wave is 268m/s
• D. wavelength of reflected waves is nearly 0.2m

Answer 1

Answer: (B), (D)

number of waves arriving per second which meets the reflected surface is 1320
wavelength of reflected waves is nearly 0.2m

${\lambda }^{{}^{\prime }}=\frac{V-V_s}{f}=\frac{332-32}{1000}=0.3m$
$f^{{}^{\prime }}=f\frac{(V+V_0)}{V-V_s}=1000\times \frac{332+64}{332-32}=1320Hz$
${\lambda }^{\prime \prime }=\frac{V-V_0}{f^{{}^{\prime }}}=0.2m$