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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 intervalobserved by a person in car B is

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 intervalobserved by a person in car B is

Grade:12

2 Answers

Saurabh Koranglekar
askIITians Faculty 10335 Points
4 years ago
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Arun
25750 Points
4 years ago
Dear student
 
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
 
Thanks and regards

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