Question

A person is standing at a train station, and two identical trains are passing each other 100 m down the tracks. Train A is moving away from him at 20 m/s, and train B is moving toward him at 20 m/s. As the trains pass each other, they emit identical pulses of sound from their horns. At the instant that the pulses are sounded, the trains' horns are both precisely 100 m away from him. What will the person hear? Group of answer choicesT

The pulses reach him at the same instant of time, but A has a higher pitch.

Pulse A will reach him first, and have a lower pitch than B.

Pulse A will reach him first, and have a higher pitch than B.

Pulse B will reach him first, and have a higher pitch than A.

The pulses reach him at the same instant of time, but B has a higher pitch.

Answer 1

As the velocity of sound is same both sound will reach at same time.

But both sound has different frequency due to dopler effect. Dopler effect states that the frequency of sound is greater than actual if either of source or observer moving towards each other and it is lower if they move from each other.

As train A is moving away from person the sound from train A has lower frequency than actual

Also train B moving towards the person it has larger frequency than actual.

If both trains A and B emitting same frequency then also sound from train B has more frequency. Higher frequency means higher pitch.

So last option is correct.