A motor car is approaching towards a crossing with a velocity of $72\ kmh^{- 1}$. The frequency of sound of its horn as heard by a policeman standing on the crossing is 260Hz. The frequency of horn is

Question

Dr. Abubacker · Accepted Answer

(b) From Doppler’s effect, perceived frequency is
$v^{'} = v\left( \frac{v - v_{o}}{v - v_{s}} ight)$
$v_{s} = 72kmh^{- 1} = \frac{72 	imes 1000}{60 	imes 60} = 20ms^{- 1}$
$v_{o} = 0,\ v = 332\ ms^{- 1},\ v^{'} = 260\ Hz$
$260 = v\left( \frac{332}{332 - 20} ight)$
$\Longrightarrow v = \frac{260 	imes 312}{332} = 244\ Hz$

Q. A motor car is approaching towards a crossing with a velocity of $72\ kmh^{- 1}$. The frequency of sound of its horn as heard by a policeman standing on the crossing is 260Hz. The frequency of horn is

Explanation

Reviewed by Dr. Abubacker

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