Question

A source, approaching with speed $u$ towards the open end of a stationary pipe of length $L$, is emitting a sound of frequency $f _{ s }$. The farther end of the pipe is closed .The speed of sound in air is $v$ and $f _{0}$ is the fundamental frequency of the pipe. For which of the following combination(s) of $u$ and $f_{s}$, will the sound reaching the pipe lead to a resonance?

• A. $u =0.8 \,v$ and $f _{ s }= f _{0}$
• B. $u=0.8\, v$ and $f _{ s }=2\, f _{0}$
• C. $u =0.8 \,v$ and $f _{ s }=0.5\, f _{0}$
• D. $u=0.5 \,v$ and $f _{ s }=1.5 \,f _{0}$

Answer 1

Answer: (A), (D)

$u =0.8 \,v$ and $f _{ s }= f _{0}$

Answer 2

(A) $u =0.8 \,v$ and $f _{ s }= f _{0}$
(D) $u=0.5 \,v$ and $f _{ s }=1.5 \,f _{0}$