A train moving at a speed of `220ms^-1` towards a stationary object emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (speed of sound in air is `330ms^(-1)`)

Options

A. 3500 Hz
B. 4000 Hz
C. 5000 Hz
D. 3000 Hz

Answer

C

Explanation

From Doppler's shift, we know for this case
`n'=n((v+v_(s))/(v-v_(s)))=1000 ((330+220)/(330-220))`
`=1000 (550/110)=5000` Hz