Two trains are moving towards each other at speeds of 20 m/s and 15 m/s relative to the ground. The first train sounds a whistle of frequency 600 Hz . the frequency of the whistle heard by a passenger in the second train before the train meets is (the speed of sound in air is 340 m/s )

Options

A. 600Hz
B. 585Hz
C. 645Hz
D. 666Hz

Answer

D

Explanation

`v.=v((v+v_0)/(v-v_s))`
Here `v=600Hz, v_D=15m//s`
`v_s=20m//s,v=340 m//s`
`therefore v.=600(355/320) approx 666 Hz`