A boy is walking away from a well at a speed of `1.0 m//s` in a direction at right angles to the wall. As he walks, he below a whistle steadily. An observer towards whom the boy is walking hears `4.0` beats per second. If the speed of sound is `340 m//s` , what is the frequency of the whistle?

Explanation

`f_(b) = f_(S) - f_(S')`
`4 = f ((340)/(340 - 1)) - f((340)/(340 + 1))`
or `4 = f (1 - (1)/(340))^(-1) - f (1 + (1)/(340)) ^(-1)`
Applying Binomial, we get
`4 = f (1 + (1)/(340)) - f (1 - (1)/(340))`
`= (f)/(170)` or `f = 680 H_(Z)`