1.

A car moves towards a hill with speed v_c.It blows a horn of frequency f which is heard by an observer following the car with speed v_0.The speed of sound in air is v.

Answer»

the WAVELENGTH of sound reaching the HILL is `v/f`
the wavelength of sound reaching the hill is `(v-v_c)/f`
The wavelength of sound of horn DIRECTLY reaching the observer is `(v+v_c)/f`
the best frequency OBSERVED by the observer is `(2v_x(v+v_@)f)/(v^2-v_c^2)`

Solution :Frequency of horn directly heard by observer `(v+v_0)/(v+v_c)f`
Frequency of echo =`v/(v+v_c)f`
Frequency of echo of horn as heard by observer.
`v/(v-v_c)f.((v+v_0)/v)`
Frequency of Beats :
`=(v+v_0)f {1/(v-v_c)-1/(v+v_c)}=(2v_c(v+v_0))/((v_2-v_c^2))f`


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