two trains `Aand B` moving with speeds `20m//s` and `30m//s` respectively in the same direction on the same straight track, with `B` ahesd of `A`. The engines are at the front ends. The engine of train `A` blows a long whistle.
Assume that the sound of the whistle is composed of components varying in frequency from `f_(1) = 800 Hz` to `f_(2) = 1120 Hz`, as shown in the figure. the spread in the frequency (highest frequency - lowest frequency) is thus `320 Hz`. the speed of sound in still air is `340 m//s`.
(4) The speed of sound of the whistle is