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 .... $Hz$.

$A$ source and an observer approach each other with the same velocity $50 \, m/s$. If the apparent frequency is $435 \, s^{-1}$,then the real frequency is .... $s^{-1}$ (Take speed of sound $v = 332 \, m/s$)

$A$ train moves towards a stationary observer with speed $34\, m/s$. The train sounds a whistle and its frequency registered by the observer is $f_1$. If the speed of the train is reduced to $17\, m/s$,the frequency registered is $f_2$. If the speed of sound is $340\, m/s$,then the ratio $f_1/f_2$ is

Two cars are moving towards each other at the speed of $50 \,m/s$. If one of the cars blows a horn at a frequency of $250 \,Hz$, the wavelength of the sound perceived by the driver of the other car is (Speed of sound in air $= 350 \,m/s$) (in $\,cm$)

An observer is standing $500 \,m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 \,Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 \,Hz$, the frequency of the sound heard after reflection from the hill (in $Hz$) is about, (velocity of sound $= 330 \,m/s$):

$A$ train blowing a whistle of frequency $320\,Hz$ approaches an observer standing on the platform at a speed of $66\,m/s$. The frequency observed by the observer will be (given speed of sound $= 330\,m/s$) $.............Hz$.