Sound of freqeuncy 1000 Hz from a stationary source is reflectd form an object approaching the source is `30 ms^(-1)`, back to a stationary observer located at the source. The speed of sound in a air is `330 ms^(-1)`. The frequency of the sound heard by the observer is :

Options

A. 1000 Hz
B. 1100 Hz
C. 1200 Hz
D. 1090 Hz

Answer

C

Explanation

The frequency of sound from the stationary source reaches the object which is approaching towards the source is
`v'=v_(0)((v+v_(0))/(v))`
When `v_(0)`= frequency of source
v= speed of sound in air
`v_(0)`= speed of the object
The frequency of reflected sound from the object heard by the stationary observer located at the source is
`v''=v''((v)/(v-v_(0)))=v_(0)((v+v_(0))/(v-v_(0)))`
`=1000 ((330+30)/(330-30))=1200 Hz`