A person with vibrating tuning fork of frequency 338Hz is moving towards a vertical wall with a speed of `2 ms^(-1)`. Velocity of sound in air is `340 ms^(-1)`. The number of beats heard by that person per second is

Options

A. 2
B. 4
C. 6
D. 8

Answer

B

Explanation

The frequency of sound heard by person after reflection upon the wall is
`v. = ((v+ u_(0))/(v - u_(0))) ` v
= `((340 + 2)/(340 -2)) 338 `
= 342 Hz.
`therefore` No. of beats heard by the person = v. - v
= 342 - 338
= 4 Hz.
So correct choice is b.