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AP EAMCET201920 Apr 2019Evening ShiftPhysicsWaves and SoundActual

A siren placed at a railway platform is emitting a sound of frequency 5 kHz . A passenger sitting in a moving train A records the frequency of the siren as 5.5 kHz . During his return journey by train B he records the frequency of the siren as 6 kHz . The ratio of the speed of train B to that of train A is

Options

  1. A242 252
  2. B2
  3. C5 6
  4. D11 6

Correct answer

B. 2

Step-by-step solution

Given, frequency of sound, f_s=5 kHz frequency of siren records by moving train A , f_A=5.5 kHz frequency of siren records by moving train B , f_B=6 kHz Now, let v_s= speed of sound For observer A , frequency of siren records by train A is given as, aligned & f_A & =f_S ( v_S+v_A v_S ) or & 5.5 & =5 ( v_S+v_A v_S ) or & 1.1 & =1+ v_A v_S aligned For observer B , frequency of siren records by train B is given as, array cc & f_B=f_S ( v_S+v_B v_S ) 6=5 ( v_S+v_B v_S ) or 6=5 (1+ v_B v_S ) 6 5 =1+ v_B v_S 6 5 -1= v_B

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