JEE Main 2015 · 10 Apr · Shift 1 · Physics Q13

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A bat moving at 10 ms $^{-1}$ towards a wall sends a sound signal of 8000 Hz towards it. On reflection it hears a sound of frequency $f$ . The value of $f$ in Hz is close to (speed of sound = 320 ms $^{-1}$ )

8258

8516

8000

8424

Answer and worked solution

Official answer: B

The bat is a moving source towards the wall and then a moving observer towards it:
$f=8000\frac{320+10}{320-10}=8000\times\frac{330}{310}\approx8516\text{ Hz}.$

Topics:Doppler effect

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JEE Main 2015 · 10 Apr · Shift 1, Physics question 13