(હવામાં ધ્વનિની ઝડપ $=330\, ms^{-1}$)
Speed of sound in air, \(v=330 \mathrm{ms}^{-1}\)
The frequency of the echo detected by the driver of the train is
\(v^{\prime} =v\left(\frac{v+v_{T}}{v-v_{T}}\right)=1000\left(\frac{330+220}{330-220}\right)\)
\(=1000 \times \frac{550}{110}=5000 \mathrm{Hz}\)