question_answer 54)

                  A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz still air. The train begins to move with a speed of \[10\,\,m\,{{s}^{-1}}\] towards the platform. What is the frequency of the sound for an observer standing on the platform?                 (sound velocity in air \[=330\,m\,{{s}^{-1}}\])

Answer:

                  According to Doppler?s effect                 \[v'=\,\left( \frac{\upsilon }{\upsilon -{{\upsilon }_{0}}} \right)\,v=\,\frac{330\,\times \,400}{320}\,\,=\,412.5\,Hz\]