A source is moving towards an observer with a speed of 20 m / s and having frequency of 240 Hz . The observer is now moving towards the source with a speed of 20 m / s . Apparent frequency heard by observer, if velocity of sound is 340 m / s , is

Options

A. 268 Hz
B. 270 Hz
C. 360 Hz
D. 240 Hz

Answer

B

Explanation

Frequency of source n=240 Hz
velocity of source `=v_(s)=20 ` m/s
Velocity of observer `v_(0)=20` m/s
Velocity of sound `v=340 ` m/s
Given both the source and the observer are moving towards each other. Hence the apparent frequency of the source is,
`n'=n[(v+v_(0))/(v-v_(s))]`
`=240xx[(340+20)/(340-20)]`
`=240xx(360)/(320)=270 Hz`