1.

A source of sound is moving with a velocity of 50ms^(-1) towards a stationary observer . The Observer measure the frequency of sound as 500Hz. The appartment frequency of sound as heard by the observer when source is moving away from hom with the same speed is (Speed of sound at room temperature 350ms^(-1)

Answer»

400 Hz
666 Hz
375 Hz
177.5 Hz

Solution :`v_(L)=0,v_(s)=-50ms^(-1),f_(APP)=500HZ` (source towards the listener)
`f_(app)^(1)=?` (source away from the listener)
`v=v_("sound")=350ms^(-1)`
General FORMULA: `f_(app)=f_("true")((v+v_(L))/(v+v_(s)))`
Convention L = listener (observer)
s = source
Case (i) : Source towards the listener
`f_(app)=f_("true")((v+0)/(v+v_(s)))""....(1)`
Case (ii) : Source away from the listener
`f_(app)=f_("true")((V+1)/(V+V_(S)))""....(2)`
`((1))/((2))implies(f_(app))/(f._(app))=(v+v_(s))/(v-v_(s))`
`(500)/(f._(app))=(350+50)/(350-50)=(400)/(300)=(4)/(3)`
`f._(app)=500xx(3)/(4)=375Hz`


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