Each of two men A and B is carrying a source of sound of frequency n . If A approaches B with a velocity u
how many beats per sound will be heard by A and B

Explanation

Apparent frequency , n. ` (c + u_(0))/(c- u_(5)) xx n`
The distance between A and B is dacreasing . So , the velocity of the listener ` u_(0) ` and that of the source ` u_(s) ` , are both positive
When A is the listener, velocity of the listener, ` u_(0) = u` ,
Velocity of the source ` B , u_(s) = 0 `
So, ` n_(A) = (c + u)/(c) xx n `
Evidently , ` n_(A) gt n`
` therefore Number of beats per socond
` = n_(A) - n = ((c + u)/(c) - 1) xx n = u/c n ` .