A car approaching a crossing at a speed of $20 \;m/s$ sounds a horn of frequency of $500\;hz$ . When the car is $80 \;m$ from the crossing. Speed of sound in air is $320\;m/s$ An observer is at a distance of $60\;m$ from the crossing on a road perpendicular to the direction of motion of car. What frequency is heard by the observer .

Question

$\begin{array}{1 1} 500.0\;Hz \\ 550.2\;Hz \\526.3\;Hz \\ 520.5\;Hz \end{array} $