Two factories are sounding their sirens at 800 Hz. A man goes from one factory to the other at a speed of 2 m/s. The velocity of sound is 320 m/s. The number of beats heard by the person is 1 s will be

Options

A. 2
B. 4
C. 8
D. 10

Answer

D

Explanation

When the man is approaching the factory ,
`n'=((v_v_0)/(v))n=((320+2)/(320))800=((322)/(320))800`
When the man is going away from the factory,
`n''=((v-v_0)/(v))n=((320-2)/(320))800=((318)/(320))800`
`n'-n''=((322-318)/(320))800=10Hz`