Question

A train is traveling away from you at 120 km/h. it blows its whistle, and you hear a tone of 0.400 kHz. Take the speed of sound to be 340 m/s. What frequency does the whistle actually produce? A) 444 Hz. B) 439 Hz C) 364 Hz D) 361 Hz

Answer 1

Answer:B)439.21 Hz

Step-by-step explanation:

Given

velocity of train
`v=120 km/h\approx 120* (5)/(18)=33.33 m/s`

frequency of train
`f_a=0.400 kHz\approx 400 Hz`

speed of sound
`c=340 m/s`

frequency from Doppler effect can be calculated by

`f_a=((c)/(c+v))\cdot f`

`400=((340)/(340+33.33))\cdot f`

`400=(340)/(373.33)\cdot f`

`f=400* 1.098`

`f=439.21 Hz`