Question

A person observes two moving trains, ‘A’ reaching the station and ‘B’ leaving the station with equal speed of 30 m/s. If both trains emit sounds with frequency 300 Hz, (Speed of sound: 330 m/s) approximate difference of frequencies heard by the person will be:

• A. 33 Hz
• B. 10 Hz
• C. 55 Hz
• D. 80 Hz

Hint:

For Doppler Effect calculations:

• Use \[ f' = f \frac{v \pm v_o}{v \mp v_s}, \] where \(v\) is the speed of sound, \(v_o\) is the observer speed, and \(v_s\) is the source speed.
• Add velocities for approaching sources, and subtract for receding sources.

Answer 1

The Correct Option is C

Frequency Observed (Doppler Effect):

• The observed frequency for train A (approaching):
• The observed frequency for train B (receding):

Difference in Frequencies:

Final Answer: \(\boxed{55 \, \text{Hz}}\)