The wavelength is $120 \, cm$ when the source is stationary. If the source is moving with a relative velocity of $60 \, m/s$ towards the observer,then the wavelength of the sound wave reaching the observer will be ... $cm$ (velocity of sound $= 330 \, m/s$).

$A$ train is moving along a semicircular track. The engine is at one end of the semicircular part of the track,while the last carriage is at the other end. The driver blows a whistle of frequency $200 \ Hz$. The velocity of sound is $340 \ m/s$. If the speed of the train is $30 \ m/s$,what is the apparent frequency observed by a passenger in the middle of the train (in $Hz$)?

$A$ 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 $f_s=1.5 f_0$

An observer moves towards a stationary source of sound,with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

$A$ source of sound is moving with a velocity of $50 \ m/s$ towards a stationary observer. The observer measures the frequency of sound as $500 \ Hz$. The apparent frequency of sound as heard by the observer when the source is moving away from him with the same speed is (Speed of sound at room temperature $350 \ m/s$). (in $Hz$)

Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of $72\; km/hr$ and $36\; km/hr$. If the first car blows a horn of frequency $280\; Hz$,then the frequency of the horn heard by the driver of the second car when the line joining the cars makes a $45^o$ angle with the roads will be .... $Hz$.