A car approaching a crossing C at a speed of 20 m//s sounds a horn of frequency 500 H_(Z) when 80 m from the crossing . Speed of sound in air is 330 m//s . What frequency is heard by an observer (at rest) 60m from the crossing on the straight road which crosses car road at right angles ?
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The value of frequency heard is 52505 Hz.
Explanation:
Given data:
- Speed of car "v" = 20 m/s
- Frequency "f" =500 Hz
- Speed of sound in air = 330 m/s
- Distance of observer "d" = 60 m
Solution:
The situation is shown as
Cos θ = 80 / 100 = 4 / 5
Apparent frequency "f(app)" = [ v / v - vs cos θ]
Now put the values in the above formula:
= [330 / 330 - 20 x 4/5 ] (500)
= [330 / 330 - 16 ] x 500
= 52505 Hz
Hence the value of frequency heard is 52505 Hz.
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