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  4. Two trains A and B are moving in the same direction with velocities 30ms- 1 and 10ms- 1 respectively. B is behind from A and A blows a horn of frequency 450Hz . Then the apparent frequency heard by observer on train B is (speed of sound is 330ms- 1 ):

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Q. Two trains $A$ and $B$ are moving in the same direction with velocities $30ms^{- 1}$ and $10ms^{- 1}$ respectively. $B$ is behind from $A$ and $A$ blows a horn of frequency $450Hz$ . Then the apparent frequency heard by observer on train $B$ is (speed of sound is $330ms^{- 1}$ ):

NTA AbhyasNTA Abhyas 2020

Solution:

Solution
$f_{app}=\left(\frac{V + V_{0}}{ V + V_{S}}\right)f=\left(\frac{330 + 10}{330 + 30}\right)450\Rightarrow f_{app}=425Hz$