# Doppler by Dimitris

**Classical Mechanics**Level pending

A train is directed to a tunnel and transmits audio frequency fs. The sound reflected from the vertical wall. The train is moving in the tunnel at a speed \(U=90\text{ m/sec}\), the observer 2 moves against the direction of the train speed \(U_2=10\text{ m/sec}\). Αt the same time the other observers remains stationary next to the train line and in front of the tunnel.

Calculate the absolute difference of the reflected frequency to which the two observers.hear the train produces a sound frequency. That is, what is \( | f_1 - f_2 | \)?

Give your answer in hertz.

Take \(f_s=1000\text{ Hz}\).

It is given that the speed of sound \(340\text{ m/sec} \).