If the source and the observer are both relatively at rest and the speed of sound is increased,then the frequency heard by the observer will:

If a source emitting waves of frequency $f$ moves towards an observer with a velocity $v/4$ and the observer moves away from the source with a velocity $v/6$,the apparent frequency as heard by the observer will be ($v =$ velocity of sound).

When the source of sound moves away from a stationary listener,we obtain $f_{L} < f_{S}$. Why?

The apparent frequency of a note,when a listener moves towards a stationary source with a velocity of $40 \ m/s$,is $200 \ Hz$. When the listener moves away from the same source with the same speed,the apparent frequency of the same note is $160 \ Hz$. The velocity of sound in air is (in $m/s$):

$A$ train blowing its whistle moves with constant speed on a straight track towards an observer and then crosses him. If the ratio of the difference between the actual and apparent frequencies is $3:2$ in the two cases (approaching and receding),then the speed of the train is (where $v$ is the speed of sound).

Two trains are moving towards each other at speeds of $20 \, m/s$ and $15 \, m/s$ relative to the ground. The first train sounds a whistle of frequency $600 \, Hz$. The frequency of the whistle heard by a passenger in the second train before the trains meet is ...... $Hz$ (the speed of sound in air is $340 \, m/s$).