A car $P$ travelling at $20 \mathrm{m} {\mathrm{s}}^{-1}$ sounds its horn at a frequency of $400 \mathrm{Hz}$. Another car $Q$ is travelling behind the first car in the same direction with a velocity $40 \mathrm{m} {\mathrm{s}}^{-1}$. The frequency heard by the passenger of the car $Q$ is approximately [Take, velocity of sound $=360 \mathrm{m} {\mathrm{s}}^{-1}$]

• A

  $421 \mathrm{Hz}$
• Correct answer
  B

  $471 \mathrm{Hz}$
• C

  $485 \mathrm{Hz}$
• D

  $514 \mathrm{Hz}$

Hence, the correct answer is option: 'B'.