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

Answer

C

Explanation

The frequency of sound from the stationary source reaches the object which is approching towards the source is `upsilon.=upsilon_(0)((v+v_(o))/(v))`
where, `v_(0)` = frequency of source v = speed of sound in air `v_(o)` = speed of the object
The frequency of reflected sound from the object heard by the stationary observer located at the source is
`upsilon..=upsilon.((v)/(v-v_(o)))=upsilon_(0)((v+v_(o))/(v-v_(o)))`
`=1000((330+30)/(330-30))=1200Hz`