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) 10 Hz (b) 55 Hz (c) 80 Hz (d) 33 Hz

Answer: (b). Train A approaching: fA = 300 × (330)/(300) = 330 Hz. Train B receding: fB = 300 × (330)/(360) = 275 Hz. Difference = 55 Hz. So the answer is (b) 55 Hz.

A person observes two moving trains, 'A' reaching the station and 'B'… | JEE Main 2023 (29 Jan, Shift 1)

Q34JEE Main 2023 · 29 JAN · SHIFT 1Easy

Doppler Effect

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

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Answer: (b)

Train A approaching: $f_A = 300 \times \frac{330}{300} = 330$ Hz.
Train B receding: $f_B = 300 \times \frac{330}{360} = 275$ Hz.
Difference $= 55$ Hz. So the answer is (b) 55 Hz.

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Doppler Effect question from JEE Main 2023 (29 Jan, Shift 1)

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