Question:
A bat moving at \(10\ \mathrm{m\,s^{-1}}\) 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 \(= 320\ \mathrm{m\,s^{-1}}\))
A bat moving at \(10\ \mathrm{m\,s^{-1}}\) 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 \(= 320\ \mathrm{m\,s^{-1}}\))
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Apply the Doppler effect twice: the wall receives from a moving source, then the bat (moving observer) receives from the wall as a stationary source.
Updated On: Nov 11, 2026
- 8258
- 8424
- 8000
- 8516
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The Correct Option is D
Solution and Explanation
Frequency received by the wall (source moving towards it): \(f_1=8000\times\frac{320}{320-10}=8000\times\frac{320}{310}\approx8258\ \mathrm{Hz}\).
The wall re-emits \(f_1\); the bat (observer) moves towards the wall: \(f=f_1\times\frac{320+10}{320}=8000\times\frac{330}{310}\approx8516\ \mathrm{Hz}\).
Answer: (4) 8516
The wall re-emits \(f_1\); the bat (observer) moves towards the wall: \(f=f_1\times\frac{320+10}{320}=8000\times\frac{330}{310}\approx8516\ \mathrm{Hz}\).
Answer: (4) 8516
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