A train travelling at 108 km h ⁻¹ towards east whistles with a dominant frequency of 500 Hz . The speed of sound in air is 340 m/s . What frequency will a passenger sitting near the open window hear?

Step-by-step solution

The passenger and the whistle are on the same train. The relative velocity between the source of sound (whistle) and the observer (passenger) is zero. According to the Doppler effect, the apparent frequency is given by f' = f ( v - v_o v - v_s ) . Since both the source and the observer are moving with the same velocity in the same direction, v_o = v_s . Substituting these values, we get f' = f = 500 Hz . The frequency heard by the passenger remains unchanged at 500 Hz .