Question

If a train approaches you (sitting in the bench ) at a velocity of 35 m/s, what frequency will you hear as it sounds its whistle at 188 Hz? speed of sound= 345 m/sA) 188 HzB) 170.7 HzC) 209.2 HzD) 202.7 Hz

Answer 1

Given:

The speed of the train is,

$v_s=35\text{ m/s}$

The actual frequency of the whistle is,

$f=188\text{ Hz}$

The speed of sound in air is,

$v=345\text{ m/s}$

To find:

The frequency heard by the observer

Explanation:

The apparent frequency when the train approaches the observer is given by,

$\begin{gathered} f_{apparent}=f\frac{v}{v-v_s} \\ =188\times\frac{345}{345-35} \\ =188\times\frac{345}{310} \\ =209.2\text{ Hz} \end{gathered}$

Hence, the frequency heard by you is 209.2 Hz.