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A policeman on duty detects a drop dete...

A policeman on duty detects a drop detects a drop of `15%` in the pitch of the horn of a motor car as it crossed him. If the velocity of sound is `330metre //sec`., calculate speed of the car.

Text Solution

Verified by Experts

The correct Answer is:
26.7
Before crossing, source is moving away from the stationary observer,
`:. v..=(v-0)/(v+v_s)xxv" "...(ii)`
Dividing (ii) by (i),
`(v..)/v-(v-v_s)/(v+v_s)`
As the pitch drops by 15% , so
`(v..)/(v.) = 85/100 = 17/20`
Hence `17/20=(330-v_s)/(330 +v_s)`
On solving, `v_s = 26.7 ms^(-1)`
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