A vehicle with a horn of frequency n is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency $\mathrm{n}+{\mathrm{n}}_1$ when he is at the shortest distance between them. Then (if the sound velocity in air is 300 m/s)

• A

  ${\mathrm{n}}_1=10\mathrm{n}$

• B

  ${\mathrm{n}}_1=0$

• C

  ${\mathrm{n}}_1=0.1\mathrm{n}$

• D

  ${\mathrm{n}}_1=-0.1\mathrm{n}$