A train moving a uniform velocity of 180km/h, approaches another train standing on a platform. An observer O moves with a uniform velocity of 36km/h towards , as shown in figure. Both the trains are blowing whistles of same frequency 120 Hz. When O is 600 m away from and distance between and is 800 m, the number of beats heard by O is x. Find x.
[Speed of the sound = 330 m/s]

Answer

8.12 or 8.13

Explanation

`f'_1=(330+10)/(330)(120)`
`f'_2=(330+10 cos 53^(@))/(330-30 cos37^(@))(120)`
`=(330+6)/(320-6)(120)`
`therefore f_b=f'_2-f'_1=((336)/306-340/330)(120
)=8.128`