$A$ whistle sends out $256$ waves in a second. If the whistle approaches the observer with a velocity equal to $\frac{1}{3}$ of the velocity of sound in air,calculate the number of waves per second the observer will receive.

$A$ sound source is moving towards a stationary listener with $1/10$th of the speed of sound. The ratio of apparent to real frequency is

The speed of sound in air at a given temperature is $350 \, m/s$. An engine blows a whistle at a frequency of $1200 \, cps$. It is approaching the observer with a velocity of $50 \, m/s$. The apparent frequency in $cps$ heard by the observer will be:

$A$ drone fitted with a siren is flying directly away from the drone operator and towards a distant building at a speed of $15 \,m/s$. The siren produces a sound of frequency $780 \,Hz$. What is the frequency that the operator hears in the echo reflected from the building (in $\,Hz$)? [Speed of sound is $340 \,m/s$.]

$A$ vibrating tuning fork is moving slowly and uniformly in a horizontal circular path of radius $8 \, m$. The shortest distance of an observer in the same plane from the tuning fork is $9 \, m$. The distance between the tuning fork and the observer at the instant when the apparent frequency becomes maximum is ......... $m$.

When an engine passes near a stationary observer,its apparent frequencies occur in the ratio $5/3$. If the velocity of sound is $340 \ m/s$,then the velocity of the engine is .... $m/s$.