A small electric train is moving in a straight line at a constant speed i$.$ To determine itsspeed, an experimenter sends an acoustic wave of frequency f $=40$ KHz towards the train. Aftersuperposing the signal emitted with the signal reflected, a pattern of beats is shown in Fig $($a$).$Determine the frequency of the beats, the frequency of the faster oscillations and the frequency measured by the experimenter.i$1)$

$($a$)s(t)$ vs $t$ for the superposition of emitted and received signals Calculate the speed o of the train. Assume T $=20\backslash$deg C$.$