A source of sound `S` emitting waves of frequency `100 Hz` and an observer `O` are located at some distance from each other. The source is moving with a speed of `19.4ms^-1` at an angle of `60^(@)` with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air `330ms^-1`) is

Options

A. `97Hz`
B. `100Hz`
C. `103Hz`
D. `106Hz`

Answer

C

Explanation

Here, `v=100Hz, upsilon_(S)=19.4 cos 60^(@)=9.7m//s`
`upsilon_(L)=0, upsilon=330m//s`
apparent frequency `v^(')=(upsilon)/(upsilon-upsilon_(S))xxv`
`:. v^(')=(upsilon)/(upsilon-9.7)xx100`
or `v^(')=100((330)/(330-9.7))=(33000)/(320.3)=103.02Hz`
`=103Hz`