A car is accelerating while its horn is blowing. Just after the car passes a stationary person, the person hears a frequency of 960 Hz. 17.5 seconds later, the frequency heard by the person has decreased to 927 Hz. When the car is stationary, its horn emits a sound whose frequency is 1060 Hz. The speed of sound is 343 m/s. What is the acceleration of the car? Assume that the velocity of the car is always in the positive direction.