A source of sound of frequency `1000 H_(Z)` moves unifornly along a straight line with velocity `0.8` times velocity of sound . An observer is located at a distance `l= 250 m` from this line. Find
(a) the frequency of the sound at instant when the source is closest to the observer.
(b) the distance of the source when he observer no change in the frequency.

Options

A. 320m
B. 278 m
C. 225m
D. 175m

Answer

A

Explanation

Frequency of pulse which is emitted at nearest point position 'B' will be received as actual (since `vec(V)_(2)botBO)`.
Let time taken by above pulse to raech the observer O is t.
Then `BO=vt=250m` . . (i)
And further distance moved by source away from point B during this time, ,br> `BP=V_(S)xxt=0.8VxxT=0.8xx250=200m` [from (i) `Vxxt=250`]
`therefore ` Required distance between source and observer.
`OP=sqrt((250)^(2)+(200)^(2))=320m`.