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The Pitch of the whistle of an engine ap...

The Pitch of the whistle of an engine appears to drop to `5/6` th of original value when it passes a stationary observer if the speed of sound in air is 350 m/s then the speed of engine is

A

35 m/s

B

70 m/s

C

105 m/s

D

140 m/s

Text Solution

Verified by Experts

The correct Answer is:
a
According to the question frequency observed by observer decreases therefore the source must be moving away from the stationary observer apparent frequency observed
`v_(a)=(v)/(v+v_(s))v_(0)`
where `V_(0)`= orginal frequency
V= speed of wave
`V_(s)`= speed of source (engine)
`rarr (5/6V_(0))=(360)/(350+V_(s))V_(0)`
`rarr 350 +V_(s)=6/5xx350=6xx70=420`
`rarr` speed of engine `v_(s)=420 - 350 =70 m/s`
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