Question

A car sounding a horn of frequency 1000 Hz passes au observer. The ratio of frequencies of the horn noted by the observer before and after passing of the car is 11 : 9. If the speed of sound is 'V', the speed of the car is ______.

पर्याय

• V

• `"V"/10`

• `"V"/5`

• `"V"/100`

Answer 1

A car sounding a horn of frequency 1000 Hz passes au observer. The ratio of frequencies of the horn noted by the observer before and after passing of the car is 11 : 9. If the speed of sound is 'V', the speed of the car is `underline("V"/10)`.

Explanation:

When the car is approaching the observer, the apparent frequency is given by

`"V"_1="V"("V"/("V"-"V"_c)),`      V_c = velocity of car

when the car is receding the apparent frequency is given by

`"V"_1="V"("V"/("V"+"V"_C))`

`therefore"V"_1/"V"_2=("V"+"V"_C)/("V"-"V"_C)=11/9`

Solving the above equation we get

`"V"_c="V"/10`