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?

$A$ train approaching a railway platform with a speed of $20 \, m \, s^{-1}$ starts blowing the whistle. The speed of sound in air is $340 \, m \, s^{-1}$. If the frequency of the emitted sound from the whistle is $640 \, Hz$,the frequency of sound as heard by a person standing on the platform is .... $Hz$.

$A$ source of sound is moving with a constant velocity of $30 \,m/s$ emitting a note of frequency $256 \,Hz$. The ratio of frequencies observed by a stationary observer while the source is approaching him and after it crosses him is [speed of sound in air $= 330 \,m/s$].

$A$ car $P$ travelling at $20\,ms^{-1}$ sounds its horn at a frequency of $400\,Hz$. Another car $Q$ is travelling behind the first car in the same direction with a velocity $40\,ms^{-1}$. The frequency heard by the passenger of the car $Q$ is approximately $.......\,Hz$. [Take,velocity of sound $= 360\,ms^{-1}$]

The source producing sound and an observer are both moving along the direction of propagation of sound waves. If the respective velocities of sound,source,and an observer are $v$,$v_s$,and $v_o$,then the apparent frequency heard by the observer will be ($n =$ frequency of sound).

$A$ 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 $Hz$)