• # question_answer A train moving with $20\,\,m{{s}^{-1}}$ towards a stationary observer produces frequency of 440 Hz. The apparent frequency heard will be ($v=330\,\,m{{s}^{-1}}$) A)  448 Hz           B)  455 Hz           C)  440 Hz                        D)  468 Hz

Apparent frequency heard by stationary observer $n'=n\,\left( \frac{V}{V-{{V}_{s}}} \right)$ Given, $V=330\,m{{s}^{-1}},\,\,{{V}_{s}}=20\,m{{s}^{-1}}$and n = 440 Hz $\therefore$    $n'440\,\,\left( \frac{330}{330-20} \right)$ $=468.38\approx \,468\,Hz$