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A man is watching two trains, one leavin...

A man is watching two trains, one leaving and the other coming in with equal speed of 4 m/s. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air is `320(m)/(s)`) will be equal to

A

6

B

3

C

0

D

12

Text Solution

Verified by Experts

The correct Answer is:
A
Apparent frequency due to train which is coming in is
`n_1=(v)/(v-v_s)n`
Apparent frequency due to train which is leaving is
`n_2=(v)/(v+v_s)n`
So the number of beats is
`n_1-n_2=((1)/(316)-(1)/(324))320xx240impliesn_1-n_2=6`
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CENGAGE PHYSICS ENGLISH-SOUND WAVES AND DOPPLER EFFECT-Single Correct
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