A person riding a car moving at `72 km h^-1` sounds a whistle emitting a wave of frequency 1250 Hz. What frequency will be heard by another person standing on the road (a) in front of the car (b) behind the car ? Speed of sound in air `= 340 m s^-1` .

Answer

A, B, C

Explanation

a. Given `v_s=72km/hour`
`=20 m/s, F=1250Hz`
Apparent frequency
`=(340+0+0)/(340+0-20)xx1250`
`=1328Hz`
For second case Apparent frequency
`=((340+0+0)/(340+0-(-20))xx1250`
`=340/360xx1250=1181Hz