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A police in a siren car moving with a velocity of 20ms^-1 chases a thief who is moving in a car with a velocity v`ms^-1. The police car sounds at frequency 300hz,and both of them move towards the a stationary siren of frequency 400hz. Calculate the speed in which thief is moving.
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  • Given A police in a siren car moving with a speed 20m/s
  • The police car sounds a frequency of 300 Hz, and both of them move towards a stationary siren of frequency 400Hz.
 
  •  Let f1 be the sound of a police car
  • f2 be the stationery siren.
  • So f1 = f2 since there is no sound.
 
  • f1 = 330 - v/330 - 20 x 300 and f2 = 330 + v /330 x 400
  • So 330 - v/330 - 20 x 300 = 330 + v/330 + v/330 x 400
  • 990 - 3v/31 = 1320 + 4v/33
  • 33(990 - 3v) = 31(1320 + 4v)
  • 223 v = - 8250
  • v = 36.99 m/s
[credit: knjroopa via brainly]
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