A stationary motion detector sends out a sound wave of frequency f= 4.0-Hz towards an approaching car. The wave is reflected off the car and the reflected wave is picked up by the motion detector. When the reflected wave is superimposed on the original wave, it is found that the sum produces a beat frequencyfbeat= 0.049-Hz. Find the speed of the car. You may assume the speed of sound in air to be 340-ms-