$A$ bus is moving with a velocity of $5 \ m/s$ towards a huge wall. The driver sounds a horn of frequency $165 \ Hz$. If the speed of sound in air is $355 \ m/s$,the number of beats heard per second by a passenger on the bus will be:

An observer is approaching with a speed $v$ towards a stationary source emitting sound waves of wavelength $\lambda_0$. The wavelength shift detected by the observer is (Take $c$ as the speed of sound).

$A$ train sounding a whistle of frequency $510 \,Hz$ approaches a station at $72 \,km/hr$. The frequency of the note heard by an observer on the platform as the train $(1)$ approaches the station and then $(2)$ recedes from the station are respectively (in hertz) (velocity of sound in air $= 320 \,m/s$).

With what velocity should an observer approach a stationary sound source,so that the apparent frequency of sound appears double the actual frequency? (Let $v$ be the velocity of sound).

When a source of sound moves towards a stationary observer,the apparent frequency heard by him

When the source of sound moves towards a stationary observer,the wavelength of sound received by him