JEE Main 2014 · 12 Apr · Shift 1 · Physics Q15

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PhysicsSingle correct+4 / -1Question 15 of 90

A source of sound A emitting waves of frequency 1800 Hz is falling towards ground with a terminal speed $v$ . The observer B on the ground directly beneath the source receives waves of frequency 2150 Hz. The source A receives waves, reflected from ground, of frequency nearly : (Speed of sound = 343 m/s)

2150 Hz

2500 Hz

1800 Hz

2400 Hz

Answer and worked solution

Official answer: B

Source approaching B: $2150=1800\dfrac{343}{343-v}$ , so $v\approx55.8$ m/s.

The ground reflects 2150 Hz, and the source moves towards it as an observer:
$f=2150\cdot\frac{343+55.8}{343}\approx2500\text{ Hz}.$

Topics:Doppler effect

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JEE Main 2014 · 12 Apr · Shift 1, Physics question 15