A stationary source emits the sound of frequency $f_0=492 \mathrm{~Hz}$. The sound is reflected by a large car approaching the source with a speed of $2 \mathrm{~ms}^{-1}$. The reflected signal is received by the source and superposed with the original. What will be the beat frequency of the resulting signal in Hz ? (Given that the speed of sound in air is $330 \mathrm{~ms}^{-1}$ and the car reflects the sound at the frequency it has received)