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. 10
B. 4
C. 2
D. 8

Answer

A

Explanation

`n_(1) = n_(0) {(v-v_(0))/(v-v_(s))}= 800 P{(320-2)/(320)}`
`= (800 xx 318 )/(320) ` Hz
`n_(2) = n_(2) {(v-v_(0))/(v_(0)-v_(s))} = 800 {(320+2)/(320)}`
`= (800xx 322)/(320) ` Hz
`:.` Beat frequency `= n_(2) - n_(1)`
`= (800 (322-318))/(320) `
`= (800 xx 4)/(320) = 10 ` Hz