Question:medium
A radar sends sound waves of frequency 'f' towards an aeroplane moving away from it. If the difference in the frequencies of waves sent and received by the radar is 10% of 'f', then the speed of the aeroplane in $ms^{-1}$ is nearly
(Speed of sound in air = 342 $ms^{-1}$)
A radar sends sound waves of frequency 'f' towards an aeroplane moving away from it. If the difference in the frequencies of waves sent and received by the radar is 10% of 'f', then the speed of the aeroplane in $ms^{-1}$ is nearly
(Speed of sound in air = 342 $ms^{-1}$)
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For reflection from a moving object, the Doppler shift formula for $\Delta f$ when $v \ll c$ is approx $\Delta f = \frac{2v}{c}f$.
Using approximation: $0.1 = \frac{2v}{342} \Rightarrow v = 17.1$, which is close to 18. Exact calculation is safer here.
Updated On: Mar 31, 2026
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The Correct Option is D
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