A car moving at `108 km h^-1` finds another car in front of it going in the same direction at `72 km h^-1`. The first car sounds a horn that has a dominant frequency of 800 Hz. What will be the apparent frequency heard by the driver in the front car ? Speed of sound in air ` = 330 ms^-1`

Answer

B

Explanation

According to the question velocity of car A
`=V_A=18 km/h=30 m/s`
`V_B=72km/h=20m/s, f=800Hz`
So, the apparent frequency heard by the car B is given by
`f^1=((330-20)/(330-30))xx800=826.9`
`=~ 827Hz`