bullets are fired at regular interval of 20s from a car A moving with 54km/h towards a car B which is approaching A with 30km/h if the speed of sound is330 m/s and that of wind is 10 m/s along BA ,then firing interval observed by a person in car B is
Asked by sirmorrudransh
16th February 2018,
8:14 AM
Answered by Expert
Answer:
Let initially when the first firing sound is made A abd B are S km aprt. Since air speed of 10 m/s is along the direction B to A, effective sound velocity is 340 m/s. if t is time taken by sound to travel S km, then t = (S/340) seconds. First firing sound will be heard by B after t seconds from the time when firing made at A.
During the 20 second interval the distance between them reduces by 467 m. ( 84 km/hr = (5/18)×84 m/s; in 20 seconds (5/18)×84×20 = 467 m)
So the sound delay is reduced by 1.4 seconds.
If sound is made at 0, 20, 40, 60....... seconds at A, B will hear at t, 20+t-1.4, 40+t-2.8, 60+t-4.2.... seconds
Answered by Expert
19th February 2018,
5:22 PM
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